Various reasons over the years:

• Don't want to risk making the workplace unpleasant (twice)
• Wrong race that would upset my parents (twice)
• Lives too far away (twice)
• Age gap (once)
• Me being exposed to porn at a very young age (first time I was 3 or 4, and I grew up with unsupervised internet access) gave me a completely broken sexuality and I don't want to bring other people into this mess
• Feeling inadequate, ugly or uninteresting (I used to be very fat so you can imagine how I grew up)
• Feeling that my interest in the other person is not genuine and that I only see her as a sexual object

In the end, I'm 32 and single, my friends are getting married and starting their own families and I have this dreadful feeling that I missed out on something important in life, I drown this feeling in work, video games and all sorts of projects, but when I'm alone and I can't think of anything to do and I start thinking about the future, I want to kill myself.