Why am I not satisfied with the amazing man that I have?

I can meet men and get dates easily but after a week or even several months of dating or being in a relationship, I begin to wonder if there is someone better out there for me. It happens with almost every guy that I've meet. Then, after I dump a guy (usually an amazing one) I regret it. I'm afraid of getting rid of every great man that comes my way and that I'll end up alone. Is it possible that I just haven't met "the one" yet? Or maybe that I'm too picky? I don't know why I start looking for someone better and not happy with the one I'm with. Even when I weigh the pros and cons of a certain man, I'm still unsure if he is the best choice possible.This seems to happen in other areas of my life as well. I don't know how to stop this bad habit. Anyone have the same problem or advice for me? That would be great.