Do you ever look back with regret? Lisa Marks examines what happens when you feel you've missed an opportunity for love

I'm not really the type of person who looks back and sighs at what might have been - it's negative and doesn't change things. But something happened recently that made me do just that. Like many other single women in their 30s, I am starting to wonder if I'm ever going to meet Mr. Right. Let me clarify this. I'm not desperate to have children, or get married, but I would like a partner to share my life. I'm hopeful that I will find him, but life is full of question marks. Is there someone out there I've already met but let slip through my fingers?

You've probably had the same thoughts. Have you ever searched for an old friend on the Internet? Have you ever wondered why you didn't stay in touch with that exciting tutor from college? Or go home with that handsome man from the dinner party? Should you have seized the moment?

A few days ago I received an email from an old friend, which got me thinking about what could have been. Dan and I were at journalism college together. We bonded because we were the two youngest on the course and had the same sense of humour. We used to hang out with each other, and everyone else thought we were an item. We weren't. I don't know why it never happened, but it didn't. I think we were scared that it might ruin our friendship, or maybe the timing wasn't right. After the course we kept in touch, but life got in the way and we saw less of each other, especially after we settled down into other relationships.

I didn't think any more of it until I got his email. Dan is now living in Rome - it was always a dream of his. He loves the Italian lifestyle and even has a column in a local newspaper. He's also in a long-term relationship and sounds very happy. I was delighted to hear from him, especially because he asked me to visit for a few days, with the proviso that I do so when his girlfriend is away, so we can 'get trashed and laugh over old times.' I was so happy to hear from him that it got me wondering whether or not I had indeed let my Mr. Right slip away. Dan is funny, good-looking, intellectual and creative. All the things I love in a man.

Another friend of mine was in the same predicament, recently. Jenny is 29 and used to work with Peter, over ten years ago. She fell for him big time but he was living with someone and, although he pushed her to have an affair, she resisted his charms and moved jobs. She says that, up until recently, she always wondered if she'd made the right move. But then came the ten-year office reunion, at the ad agency where Peter still works. 'I saw Peter across the room and, although he still had that twinkle in his eye, he had put on weight, was balding and really quite dull. I always remembered him as being so vibrant and witty that it shocked me. It was good to see him, though. We talked fondly about old times. But I realise now that I made the right decision. If I had got together with Peter, I wouldn't have lived such an interesting life.'

On balance, like Jenny, I don't regret not getting together with Dan. Although we're best friends, we would have made terrible lovers; we're too alike. I think it's also fair to say that a lot of positive things came out of our friendship, which an romantic relationship would have jeopardised. At the time I was a very unconfident 18-year-old, and being close to Dan gave me the boost I needed in order to make my own way in the world.

If you find yourself stuck in the past, try and put these feelings into perspective.Nostalgia is a strong emotion, but it's often misleading. It's far better to live for the moment. Instead of regretting the past, learn from it. Use the experience as a signpost to finding the real Mr. Right. If you're now sure of what you're looking for, then you won't miss out the next time. Dan has come back into my life, but people change. I may well set eyes on him and breathe a sigh of relief - or will I?