One of the things you have to realize is that when relationships end, it's truly not anybody's fault. Relationships end because there is a conflict between who you are and who the other person is, and that conflict ends up being unresolvable. Because of this inability to reconcile whatever conflict that exists, the relationship goes through phases where the cracks begin to weaken and come apart. This conflict causes people to do things that we eventually look back on and regret. We try to assign blame, but the real blame is the incompatibility that exists between you.

There's no shame in being unable to reconcile an incompatibility. Very few people that you date will be a good match for you. Everyone else will be a series of failed matches, some spanning months and years and others fail rather quickly (such as the first date, for instance).

What is important is that you look at your reactions to these failed relationships and find your insecurities. It's very clear you have insecurities surrounding girls. You worry so much about making them like you that you forget to even ask yourself if you like them. This need to please (such as your mentioning the sex) indicates a whole host of things you believe about yourself that, if you have the courage to look at them, could open you up to growth and change. You can find your confidence again, but it requires you to give yourself permission for a time to be insecure.

And for the record, most women don't care how long you last during sex. What matters to women is the total experience, not just the amount of time you had yourself inside of her. If you can't last long in that regard, you can add to the experience by giving her oral pleasure, kissing her neck, etc. Most guys, I think, get so worried about the actual sex part that they forget that most women enjoy the overall sexual experience. So, don't sweat it.