I am a single man, because I choose to be. The same thing happens to me quite often. I have dated many women, and had many girlfriend, but I have choosen to be single while going through school. I work and go to school, both full time. I really just don't have time for a relationship.
I also do not want any children, and never have. Some of my relationships have ended for this very reason. People think that I am being selfish, but I do not know why they feel that I should want children, and I don't understand why that is selfish.
I beleive the reason that people try to push relationships on other people is because society dictates that people are supposed to get married and have children, or they may not understand how someone can be happy while not in a relationship. I do not need a relationship to make me happy.