Why can't he find me?

Yesterday, my good friend and roommate got engaged to her boyfriend of five years. I couldn’t be happier for her, we went out and bought bridal magazines, balloons, her favorite cookies, and made congratulatory banners for our doors. That being said, while I am very happy for her, it also makes me slightly depressed. I have never been in a real relationship, I either screw it up before it begins or I push them away or they loose interest.
I want to find someone that I could someday marry. I know that I have plenty of time to find someone, I’m only 22. I just don’t understand why I never have the opportunity to be with someone. I think I am decently pretty, smart, and fun. I see people around me who are not very nice people, but somehow they have still managed to find someone. It just makes me wonder what is wrong with me. Should I just forget about this? Am I taking things too seriously? (It wouldn’t be the first time) Or do I actually have a valid point? Could there be something I am subconsciously doing to repel men? What can I do to be more open to people?