How does it feel when you discover your marriage is a lie? Ask former New York City actress and model Jen Waite, 32, who has written a powerful memoir, “A Beautiful, Terrible Thing” (Plume, out Tuesday). She tells The Post’s Jane Ridley how she unmasked her “perfect” husband as a liar — and ultimately gained strength from the ordeal.

Holding my 3-week-old baby, I open our laptop for the first time since her birth. I click on a sent email from my husband Marco’s account with the subject line: “Appointment.”

It was delivered to a real estate agent, then forwarded to a woman called Viktorja. “My girlfriend and I have decided to go with another apartment, but thank you for your time,” it reads.

I almost laugh out loud. My first thought is: “Why is Marco still calling me his girlfriend after we’ve been married for two years?”

It turned out that the email, which I found the night of Jan. 20, 2015, altered the course of my existence. It wrecked my idyllic world as a new mother with a beautiful daughter and seemingly devoted spouse.

I first met my husband in June 2010 when we both worked at a restaurant in Queens. I was 25, and he was 32. An immigrant from Argentina, he confided that he was in the States illegally but stayed because he had a 7-year-old son, Seb, from a previous relationship.

He had intense, dark eyes, and he looked at me in a way no one had ever done before.

“You know, I hadn’t allowed myself to be hopeful about ever being happy again until I met you,” he told me the night of our first kiss. I was giddy with the adoration.

He proposed in front of my family during Christmas 2012, and we had a City Hall wedding in Manhattan the following February. We then started the green card process to legitimize Marco’s status in the US.

In spring 2013, we went into business with another couple to open a gastropub in Queens. I plowed $75,000 of my savings into the venture and my parents contributed $25,000. It had always been Marco’s dream to own a restaurant, and it had finally come true.

But cracks developed between Marco and our business partners. Within months, he pulled out of the arrangement and started a new job as a full-time restaurant manager in Manhattan.

By then, I was preoccupied with arrangements for our formal wedding ceremony set to be at my parents’ home in June 2014 — and 14 weeks pregnant.

Our daughter, Louisa, was born at the end of December 2014. It was a long labor and Marco kept disappearing to make phone calls to the restaurant.

Then, a few days after I was discharged from the hospital, Marco suggested Louisa and I go north to be with my parents in Maine.

“[My boss] won’t let me take time off so it’s better you’re with your family,” he said.

Two weeks later, we returned to Queens, and soon after, I found the mysterious email. Marco and I shared our passwords, and I quickly found the name Viktorja among his Facebook friends.

Her profile picture was that of a glamorous blonde of around 22, black sunglasses perched on her nose, glossed lips pursed into a duck face. I needed answers — fast.

‘All those times I’d felt vulnerable and overwhelmed being pregnant or with the baby, he’d been with another woman.’

Calling Marco at the restaurant, I was struck by his calmness as I bluntly accused him of an affair.

“Baby, first of all, trust me. I would never, ever cheat on you,” he said. “You are my life, OK?”

He explained that Viktorja was a European co-worker with no savings or credit rating. She was having trouble finding apartments as brokers weren’t taking her seriously. She’d asked Marco to contact them on her behalf.

“I was really trying to help [her] … I am so sorry, babe. I’m an idiot,” explained Marco.

An hour later, when he came home, he was no longer remorseful. He said: “For around a year now, I haven’t been happy. I lost all my feelings. I think there’s something physically wrong with me.”

I was blindsided. I’d just had a baby and my head was all over the place. Why was my husband dropping this on me now?

Even though Viktorja texted me denying anything between them, I later found an email she’d sent that included a link to an article about falling in love. Marco insisted Viktorja was studying psychology and had sent it to him innocently. Then, I stumbled across a soul-searching text he’d sent Seb’s mother, saying that he was afraid of losing Louisa but not me.

Next, he started using “gaslighting” techniques to make me question my own sanity, saying it was all in my head because I was hormonal. Though I’m not a mental-health professional nor can I make clinical diagnoses, I later found out that this is classic sociopath behavior. [Marco did not respond to requests for comment.]

Eventually, Marco confessed to an “emotional affair” with Viktorja. However, for the sake of Louisa and our marriage, I resolved to try and put it behind us. But, days later, I packed a sleeping Louisa into the back of the car and parked outside his restaurant at closing time. Two shadowy figures appeared from the doorway — Marco and a blonde I immediately recognized as Viktorja. He put his arm around her as they walked to a bar.

I finally fled to Maine to put some space between us and Marco. There, after examining our phone records, I found that, during my labor with Louisa, Marco had spent 45 minutes on the phone to Viktorja.

He’d been having an affair for months, with late-night Uber trips to Viktorja’s apartment in Brooklyn after he finished work, and they’d been hoping to rent a love nest together. All those times I’d felt vulnerable and overwhelmed being pregnant or with the baby, he’d been with another woman.

It made me sick to think I’d fallen for his lies.

He came up with fanciful excuses — also typical of a sociopath who has no feelings for anyone else but himself — and continued to deny any physical relationship. He did this right up to the time he posted a picture of him and Viktorja as his new Facebook profile.

People associate the word “sociopath” with murderers, but there’s a wide spectrum. Common traits include charm, impulsiveness, no guilt or shame, inventing lies and the inability to apologize.

It’s been over a year now since I divorced Marco. As far as I know, he still has his green card and is living in this country. As for telling Louisa what happened, I believe in being honest but in an age-appropriate way. She’ll be able to read my memoir when she’s older.

It’s taken me a while to accept what happened, but I’m much stronger now. I’ve grown into myself, am more independent and think on a deeper level. Meanwhile, I am devoted to Louisa, now 2½. I love watching her develop into an inquisitive child in our new home in Maine, where I have a stable job in insurance.

I hope my story will help other women involved with narcissists such as Marco. It proves that you can break free and lead a more fulfilling life without them.

* All identifying details and names except Jen Waite’s have been changed.