I spend hours wishing I could go back in time and play my hand differently

"I have suffered from depression for a long time, and take seroxat to cope. I have always had low self esteem. I come from a family where everyone is successful, every one apart from me that is. I also have never really had a proper relationship with a woman. Sure I have had many one night stands, but I rarely really fancy a woman (in that I would like to have a relationship with her) and on the rare occasions that I have I never had the courage to ask them on a date.
Now I am massively upset. The problem is a woman called Claire. She was a work colleague of a friend of mine. I fancied her the moment I first met her in the pub arms where her and my friend were having a drink after work. She is beautiful, clever, happy, demure but very done to earth and modest.
Over the years I met her a few times, once I chatted with her in a bar for a while and I liked her even more, but at the time she had a boyfriend. Once I went to her birthday and that was embarrassing I felt she knew I fancied her and all her mates were there.
Then one night in another bar she tried to chat to me before she left but I didn’t say much. Now I wish I’d then had the courage to ask her out. Another time was in a wine bar again she chatted to me, but again I did not have the courage to ask her out.
Each time I did not have the confidence probably due to I was only a student at the time or my job at the time was very low paid, and I felt I had no prospects.
Then she started going out with a guy, first she moved in with him. Then one night came the bombshell, he had asked her to marry him. My friend told me that she told him not to waste money on a ring, this made me love her even more. My job prospects had now improved and I now even owned my own flat.
Finally she left the UK to live with him in Hong Kong. Then my friend dropped the second bombshell that she is now pregnant.
I had always hoped I may one day marry her and now I realise that that is never going to happen. I fantasize, every minute it seems, that we are married, and how lovely it would be, only to brought back to reality and the sense of euphoria to become one of immense depression.
I spend hours wishing I could go back in time and play my hand differently, and asked her out when I had the chance; to the point it drives me crazy. I feel I had the chance and I blew it.
I now feel I will always lead a lonely life as I have no interest in other women as I compare them to Claire and they always fall way short. I feel extremely low even suicidal at times, I feel like a zombie that is just existing not living."

Source: http://how-to-get-a-girl-to-like-you.net/i-am-feeling-suicidal-i-need-to-know-how-to-get-over-a-girl-i-fancied-who-is-now-married-with-children.html