I don't remember the exact moment I realised my husband was famous. Maybe it was when a paparazzo ran backwards snapping at us with a long-lens camera as we took a stroll with our baby. Perhaps it was when the Daily Mail wrote a gushing article about "Prof Cox the Fox". Though when he turned up as a question on University Challenge, I finally had to concede that he'd actually become "one of those people off the telly".

When we first met, I was the expensively groomed television professional, working on mostly science and technology shows, and he was the newly appointed physics academic with a student's wardrobe and a single bed. All that remained of his music days with D:Ream were a few William Hunt suits in his wardrobe and framed backstage passes on his bathroom wall. It may have been my love of the Apollo moon missions or him telling me he worked at Cern, but we instantly struck up a geeky friendship. Together we started writing ambitious documentary ideas with the sole aim of "making science part of popular culture". Fast-forward 10 years and we're a lot closer to our goal, but it's not quite how I imagined it would be.

When Brian first started appearing on TV, he was more of a cult figure than a celebrity. People would occasionally come up to him with a question about black holes or the Higgs boson, having seen him on Horizon or This Morning. The only time he was asked for his autograph was after a talk he'd given in a school, or occasionally at a nerd gathering such as Skeptics In The Pub. Then he presented Wonders Of The Solar System and everything changed.

Wherever we went, people would stare, take photos with their phones or shout his name excitedly from passing cars. The novelty wore off, however, when it began to feel as though people were intruding into more private moments. In Sainsbury's, a couple of giggly middle-aged women ran up and thrust pieces of paper at him to sign. As Brian chatted to them about the physics A-levels their children were taking, I tried surreptitiously to sneak a pack of sanitary pads into our trolley. I needn't have bothered. I could have juggled a few boxes of tampons while whistling the theme tune to The Sky At Night and they still wouldn't have realised I was there.

A few years ago, I started to notice that the more Brian appeared on TV, the less interesting I became to other people. I started to morph from Gia Milinovich, independent woman with her own life and separate bank account, into "Mrs Brian Cox", then into "wife". Pre-fame, I was asked for my opinions; now, I'm asked what Brian thinks. During a discussion recently, someone said to me, "You only think that because your husband is a physicist", as if I am now incapable of my own thoughts. I am in the throes of what Edna Healey, Denis's wife, called Invisible Wife Syndrome.

As the importance of my brain declines, the focus on my physical appearance feels hawk-like. I am a mother with a young baby. Even at my most attractive, I feel frumpy, lumpy and overweight. When we were "papped" pushing the buggy, I was wearing no make-up and a breastfeeding T-shirt one size too big. After that day, with fears of the photo turning up in Heat above a comment about the "wonder" of Brian's dowdy, bovine wife, I went out and bought a ton of make-up. Now, at the very least, I put on a bit of mascara and some lipstick when I go out of the house with Brian. I've even started brushing my hair.

I worked for film producer Andrew Macdonald a few years ago. My favourite thing about him is that, even after having five kids together, he still talks about his wife Rachael Fleming as if they've only just started dating. I turned to her for advice. "The worst time was when Andrew had lunch with Cameron Diaz and he invited me along," she said. "After lunch, we all walked out of the restaurant and our picture was taken by the photographers outside. It was published with the caption 'Cameron Diaz, film producer Andrew Macdonald and friend.' Not wife, just friend. It was soon after I'd had our third child, so at least it didn't say 'fat friend'."

It's a strange dilemma. On the one hand, you don't want your husband's public life to encroach on your private life. On the other, you would like your existence, at the very minimum, to be acknowledged. As your partner is out in the public eye, you are keeping your shared "real life" afloat, often single-handedly. He needs clean pants, I wash them... it's dull, it's not glamorous, but it's a vital part of the whole package that is "Him".

While Wonders was on TV, it seemed that everyone was declaring their love for Brian: young girls, older women, gay men, even throngs of straight men admitted to having a bit of a man crush on him. At one point, on Twitter, Sarah Cawood asked Lauren Laverne to set her up with Brian, as he'd been on her show that morning... All I could think was, "Really? He used to be a bus spotter. Sure, he's cute, but he really is a massive nerd." Later that day, the baby threw up on me, so I tweeted to Sarah Cawood that I'd be very happy to share my husband with her 50/50, if she took over the baby vomit cleaning duties. Unfortunately, she declined.

When Cheryl and Ashley Cole split up, a list of possible new partners for Cheryl made the rounds on the web. Brian was on it. Silly as it may sound, I felt a bit jealous. I've also been unsure how to react when people email me to tell me they hate my husband; when two separate people "jokingly" told me they wished me dead so they could have him; and when another said she was going to marry him when he divorces me. As time goes on, I'm finding it easier to deal with, but when I saw a tweet from someone telling their friend they were currently in bed with Brian, I am ashamed to say that I actually turned to check he was still in bed with me.

As I sit here and write, Brian has been in Africa for two weeks filming his new series, Wonders Of The Universe. He will be back again in just over a week, then will spend a month working on his next book, after which he will go off filming again... And on and on it will go until he finishes filming in November, when he will be busy with something else, no doubt. The reality is that I spend 90% of my time on my own with the kids while he's out spreading the word about science.

It's the curse of every wife – or husband – of a successful person, famous or not. You marry someone because you want to spend the rest of your life with them, and soon realise that "the career" is going to take up most of the rest of their life, not you. There are, of course, obvious benefits, but when you're eating dinner on your own for the thousandth time, success, fame or money don't make it any easier to swallow. Though, admittedly, the wine is much nicer.

In order to remain sane, I need to keep my own identity and life separate from him. As Brian has made such a popular and critically acclaimed series, I am nervous about venturing back into television myself. I fear that anything I do would be unfairly compared with what he's done. Also, now that I am simply just "the wife of a celebrity", the only accepted way into television is to lose a stone, dye myself orange and demand a place in the jungle where I could shower in my bikini, then release a fitness video. The respect for my professional abilities has declined in inverse proportion to the number of Google searches for "Is Prof Brian Cox divorced yet?"

The first signs were there five years ago when Brian and I went to pitch some ideas to a producer at a well-known production company. I'd had a science-technology series broadcast on Channel 4 several months earlier, and Brian's appearances as the science expert on This Morning were going very well. Our agent called us the sci-tech version of Richard and Judy.

From the start, the producer's attention was on Brian. Every time I spoke, he'd look at me as though I was interrupting their conversation. At one point, I came out with what I thought was an excellent idea. The producer again turned towards me, said nothing and then turned slowly back to Brian. About a minute later, Brian repeated my idea almost word for word and the producer told him it was brilliant.

As we left the building, I angrily told Brian how awful the whole experience was for me. Of course, he hadn't noticed a thing. As far as he was concerned, it was a very successful meeting with a very interesting, and interested, man. I told him I felt my very presence was upsetting their budding bromance, that I was some unwanted tag-along girlfriend. "I felt like bloody Yoko Ono in there!"

Several years ago, when I was working on a music programme, I'd wear a Yoko Ono T-shirt just to annoy the musos on the production team. I'd tell them my favourite Beatle was Yoko and watch in delight while their faces went bright red with anger. I wasn't lying though.

Yoko was, and is, interesting in her own right. She's a remarkable artist and a unique thinker. All of the things you think of John Lennon doing in the late-60s and early-70s were inspired entirely and directly by Yoko: the avant-garde art, the politics, the whole peace and love thing. She is responsible for the Lennon we remember and love today, and yet she is at best ignored and at worst vilified... For what, exactly? Being loved by him?

After Brian and I had a couple more meetings with TV producers, at which I was somewhere between "invisible" and "tolerated", I decided to move on from television to produce websites and write more. Though I've accepted that Brian and I will probably never make any of the programme ideas we wrote when we first started working together, I'm happier not being the Yoko in our partnership.

And now, several years on, here we are. Brian has made a well-loved science series and I, well, until I work out how I fit into all of this, I'll just continue washing his pants.