In 2002, I decided to leave my husband. There was only one argument, really, that I remember. In mid-November, on a Sunday morning, Stig called to ask what I was doing that day. He'd been up early, making rounds at the hospital. "Thanksgiving is Thursday," I said. "I've got to bring the decorations and the turkey dishes up from the storage locker, and I was going to take the boxes that are piled up in the dining room downstairs, get them out of the way."

Stig didn't reply.

"You know, the lift is broken," I said.

"How dare you."

"Excuse me?"

"How dare you ask me to help you. I bring home the bacon. I don't ever want to be asked to help do anything around the house."

I hung up. My hands shook. The rage in his voice was out of proportion to a few boxes to be carried to the basement. And who said stuff like, "I bring home the bacon"? It was irrelevant. I'd worked or been at university our entire marriage. As had he. But it was a pivotal event. He stopped talking to me. And I stopped sleeping.

I didn't have money of my own; Stig had made sure of that. Then, miraculously, my medical practice offered me a job. I wrote Stig a letter, and put it on his desk – talking to him directly never worked out as planned. Plus I'd stopped sleeping in our bedroom and seldom saw him if and when he came home. One morning I walked into our bedroom. He was at the desk, working on his laptop. He quickly closed it when he saw me.

"What do you think about the separation?"

It had been two weeks since I had given him the letter. Stig just stared at me. He looked like someone I'd never seen before. His expression seemed scrunched, pinched, so taut that no blood could flow to the surface. His face held rage. "That's fine," he said.

Twenty years, two children and that was it. No discussion, just "fine".

A few days later, I moved to our weekend house in Michigan. When I came back to Chicago to meet an estate agent, the building engineer mentioned that my husband's girlfriend looked, from behind, just like one of my daughters. That's how I found out he had a girlfriend.

I lived in our weekend house for the summer, waiting for my job to begin, waiting for our apartment to sell. In the months after I left, after 20 years together, when I hadn't yet learned what the narrative would be, I didn't know about the girlfriend – or all the girlfriends, rather, all I knew was that he had turned into someone I no longer knew or trusted. I could barely stop crying long enough to drive my car to the off-licence. I took it there frequently. I couldn't sleep unless I drank half a bottle of wine before bed. I cried until my head ached. I had headaches every day.

Then, in a few brief weeks over the summer, the apartment sold. In September, my daughter Ruthann, who was still at high school, and I moved into a two-bedroom apartment with no view, high ceilings and large rooms. After a day of moving, my phone rang. "Margaret, this is Leo Kennedy." Leo Kennedy was a friend of my former brother-in-law. I hadn't seen him in years. "I've been wanting to call for months, ever since I heard you were separated. I'd like to take you to dinner." He was at least 70. Maybe older.

"Leo, it's just too soon for me," I said.

"I'll wait. I'll wait three weeks, then call?" I suppose Leo didn't have a lot of time to waste.

I let Leo go to voicemail for the next couple of weeks, but I registered the wake-up. Does anyone plan on being single at 44? One night I took off my clothes and stood in front of a full-length mirror. The lighting accentuated my cellulite and wrinkles, made me look depressed and a bit criminally insane. I looked like a woman who'd been left in middle age, even if I had done the leaving.

On a Saturday afternoon I was on the internet, shopping for things I didn't need. A screen popped up: match.com. I did not know how to meet men. I didn't go to bars, I was paralysed with shyness and almost all my friends were married or gay. The internet seemed a good place to start. As I read the profiles, I recognised some very angry people. They sounded like me, or like the me I didn't want to acknowledge. I would have to be careful.

I started slow. Anyone with even a passing resemblance to Stig, I immediately deleted. Then there was an email from Ed, a doctor of psychology. This was important to me because I thought it appropriate to date men as educated as myself. There's no box to check for that on match.com.

We met at a bar. "Tell me about your research," I said.

"I study sexual behaviour," Ed answered.

"Ah," I said, nodding. Of course he did. Our talk was relatively serious, in contrast to our emails, which were funny. His sense of humour seemed limited by his… person.

"So how does this work," I asked, "this dating thing?"

"Well," he hesitated, "I've dated a lot of women. And what usually happens is, after a month of sleeping together, I find a way to extricate myself from the relationship. And it's painful. Because even if the woman says she's just interested in something casual, she gets hurt. I think a woman's interest in a man grows once they're sleeping together, whereas a man stays interested for about a month, then he stops. There's actually hormonal evidence to substantiate this scenario."

This guy was every woman's worst nightmare. He was using scientific research and probably US government grant money to justify being a jerk.

"What about fun?" I asked.

"Fun is important, but sometimes I think it helps to get sex out of the way first. We could do that tonight, if you like." He looked hopeful and innocent. Or, rather, he looked like a caricature of innocence.

"Thanks, but I'm fine," I answered.

Following my aborted rendezvous with Ed, I met Angel, a banker, who arrived 20 minutes late at a coffee shop. He appeared sweaty and dishevelled, his face covered with tiny lacerations. "I have obsessive-compulsive disorder," he said. "The reason I have so many cuts on my face is because I shaved six times before I came to meet you." I nodded. "Huh," I said.

Hank, a securities analyst, took nondescript and made it a superlative. Lunch went reasonably well, and Hank was dull but showed no obvious signs of self-mutilation, so we decided we'd meet the next night. That evening he called and said he'd been fired. "Can I make dinner for you?" I offered, feeling terrible for this man I had just met. I invited a total stranger to my apartment.

Besides being fired, he told me about his prostate troubles, gastrointestinal difficulties and recent gum surgery. His ex-wife had left him for another man. It was like having dinner with Eeyore, if Eeyore had been constipated, couldn't pee and had gingivitis. By the end of the evening, I was ready to leave him, too.

In summer 2004, two years into divorce proceedings, with no end in sight and legal fees mounting, I met a businessman named Nigel through a neighbour who described him as "good-looking" and intelligent. Consider "good-looking" a subjective adjective. We met at a lovely Italian restaurant. Immediately, he asked if I liked poetry and pulled out what he called his "favourite" book of poems: The Poetry Of Richard Milhous Nixon. It contained, in poetry form, excerpts from the Watergate tapes. I was relieved. I thought, he has a sense of humour – this might work out. It was the last funny thing he said or did for two months.

I decided to have sex with him. Maybe he would redeem himself. And I was not thinking clearly. Luckily, sex turned out to be the clincher. After removing his shirt, I got the distinct impression that Nigel had not bathed. This turns some women on. I am not one of them.

After Nigel, I decided to try match.com again. There were so many issues I did not want to deal with. I did not want to face the fact that Ruthann would soon go to university, leaving me to live alone for the first time in my life. I did not want to consider why I'd stayed married for 20 years to a man I did not like. And now here I was, dating men I found unappealing, hoping they would like me. Once again thinking that the right relationship could fix my life. It never occurred to me to ask myself, how do I fix this?

In late September, I received a match.com email from a man named Alex. He told me about himself in a way that was articulate, funny. We met in early October. We talked for three and a half hours; he told me he'd lost his wife after a long illness. Still we managed to laugh. I'd finally found someone I liked. I emailed, saying what a wonderful time I'd had, offering to make dinner. "I haven't had anyone cook a meal for me in a couple of years," his email said. "I don't know if I will know how to act, so tread cautiously."

I did not take his advice. I wish I had. Alex had disaster written all over him. It had been six months since his wife died; for complex reasons, he had only begun to grieve. He treated me as a temporary player in his life, introducing me as his "date" after we'd been together for five months. He grabbed me in public, as if he were a schoolboy, sliding his hand under my skirt when he thought no one was looking. When I objected, he withdrew behind a wall. After an argument, he told me, "I don't love you, and I never will." We hadn't been talking about love. After six months, I asked if he would be available to have dinner for my birthday. "No," he said. "I'll be out of town." What about the week after? "I'll be gone then, too." Silence. I heard the sound exactly as he intended it.

In August, at the age of 88, Mum fell into a creek while playing golf. We felt quite lucky she did not lose consciousness and drown. I had her transferred to my hospital, where surgeons operated to stabilise her neck. My sisters and I decided to move her into a retirement home. We needed to get her used to the idea, but the surgery had left her demented. "Stop treating me like a chicken!" she cried when I visited her that day. My normally sweet mother had transformed into a harridan.

I thought, if this is the future, the future looks grim indeed. I slid into a depression that held on to me tight. Had it not been for my daughters, I might have let go. My despair felt interminable. I knew something had to change. I could not continue doing what I'd been doing.

I told work that I wanted back into the partnership track, to be full time. I made plans to travel. I quit match.com and ordered expanded television with classic films. I became comfortable staying home on Saturday nights by myself. Responsibilities accumulated, friendships multiplied; the lack of a relationship in my life seemed almost unnoticeable.

After four or five months, several friends offered to fix me up. I hesitated. Then one told me about a dating service she'd used. It's not cheap, she said, but when people have to go through an interview and shell out money, they're more likely to be serious about wanting a relationship.

Charles was the fifth man I met through Dating Alliance. I felt unaccountably nervous – doubtful that I'd like him, afraid that I would. I'd met so many weird men by that point. He was originally from the Netherlands and owned a manufacturing company. He spoke several languages. He was tall, maybe 6ft 5in, bald, with a skinny, white, handlebar moustache, and he looked every day of 60. Perhaps older. He asked if I'd join him for dinner. "I told the women at Dating Alliance my concern about dating someone with kids, but they assured me your kids are older."

"Why don't you want to date anyone with kids?" I asked.

"Because they always come first," he said.

Ah, I thought.

"What about your work?" he asked. "Are your hours predictable?"

"No," I answered.

He looked unhappy. I almost felt sorry for him.

When we left the restaurant, a homeless man walked up to Charles, who took out his wallet and handed him some money. I heard him murmur, "You're not going to drink all this, are you?"

"No, sir, I'm not."

"Can I call you?" Charles asked me. I wasn't attracted to him. He was controlling, probably narcissistic, one more of the same old same old. Then again, I just wanted to date. Casually. Have some fun. So I said OK.

He asked me out that Friday night. We walked to a sushi place. I was exhausted. Conversation felt like work, and I'd already spent 12 hours in the operating room. After, we walked back to my apartment. We were discussing the upcoming election, standing in the kitchen, then wandered into the living room. We sat on the sofa, facing each other. Suddenly he yanked me towards him, put his mouth on mine, roughly, holding my neck tightly.

"Wait!" I said.

"You want me to stop?" he asked.

"Yes!" I said. "I want you to stop."

I turned my head. I wanted to get a breath that didn't include him, didn't include his scent, but for that moment, I must have relaxed and the tension must have lessened imperceptibly. It was enough. He flipped on top of me and yanked my trousers down. I said again, "Stop." He was huge and heavy. I thought, if I fought him, he might hurt me more, so I said, enunciating clearly, as if to a child, "Charles, if you do this, I will never see you again. Is that what you want?"

"No," he said. He shoved himself inside me.

Afterwards, I opened the door, he walked out, and I quickly locked it behind him. I felt the numbness of shock.

Rape can make a person catatonic. It did that to me, initially. Days passed. Weeks. I barely blinked. I lay in bed without sleeping. I repressed every thought, every feeling. I did not answer Charles's calls. He rang and left messages for a week or so, then stopped. Rape stays with you – the violence and the fear – it stays with you, in small and large ways, and it screws up your life and your relationships for years. But while it is a sexual act, it is only marginally about sex. It is an assertion of power, an act of intimidation.

Margaret Overton: 'Rape can make a person catatonic. It did that to me, initially. Days passed. I barely blinked. I repressed every thought, every feeling.' Photograph: Peter Hoffman for the Guardian

The only relief I found was in riding my bike, the constant motion of it. I rode every day I could – along the lake front, in Michigan on day trips, in the suburbs when I visited my mum. Eventually, I made plans. I had a week of holiday in October and decided to take a bike trip. Although I'd done these cycling vacations before, this one marked my first time alone. I felt awkward. A younger woman, in her late 30s, thin and very fit, stuck out her hand. "Hi, I'm Micheline," she said. "Margaret," I said. A dark-haired man walked up to us, in biking gear and a jacket. "Henry," he said, "from New York," and held out his hand. "Margaret," I repeated, and shook it.

The roads, that first day, were empty, the sky blue. The group quickly spread itself out. I had no interest in hurrying and I planned to bike alone, at my own pace. Henry cycled with me, or behind me, all day. He asked questions. I answered, briefly, to be polite, and gradually the beautiful day and his genial company lifted my mood.

The second day we rode toward the coast. Once again, Henry rode with me. That night at dinner, he ordered wine for us. He asked me questions all evening. By the time dessert arrived, I felt exposed and exhausted. The next day, he apologised. He seemed to recognise his intrusiveness of the evening before. He rode beside me again, but he kept the conversation light. I thought, he seems like a good guy. But I knew I had bad judgment. And you cannot know someone in three days.

We ate dinner with the group, then left the restaurant and went for a walk. We stopped in a pub for a drink. As soon as we sat, Henry turned my barstool to face him. He took my hand and studied me intently. "Margaret, can you live in the moment?"

I frowned slightly. "I'm not sure I know what you're asking," I said. Much later I realised what I should have suspected then. His question had nothing to do with living in the moment. It had everything to do with sex, meaning sex with no strings attached. But there could be no such thing for someone like me, after all I'd been through, at that point in time, with someone like him.

Henry's divorce commenced soon after the Napa Valley trip. We saw each other over the next four months, and spoke nearly every day on the phone. We lived in different states. I stayed cautious and circumspect, or I thought I did. Then, one day, in the middle of discussing hotel reservations, Henry said he couldn't see me any more. His coldness stunned me. I sent him an invitation to my 50th birthday party six weeks later but he declined. I never heard from him again.

I feel confident that you would like a Hollywood ending to this story. I wish I could give it to you. But I'm afraid you would need to think in terms of independent films, not your typical big-studio romance. I stopped dating after Henry. I began writing and recognised my own patterns of behaviour, behaviour that seems obvious and destructive in retrospect. I gave up the internet, though friends still tell me it's the only way for a woman my age to meet a man. I find that incredibly depressing. Growing old is not for sissies. On bad days, I think I've made every mistake out there and know to anticipate the worst. On good days, I know I am lucky to be alive. Every day I wish that wisdom were not accompanied by receding gums, memory loss and joint deterioration.

• This is an edited extract from Good In A Crisis: A Memoir, by Margaret Overton, published next month by Bloomsbury at £12.99. To order a copy for £10.39, including UK mainland p&p, go to guardian.co.uk/bookshop, or call 0330 333 6846.