What happened to being yourself in a relationship (my fellow guys please answer)?

Im going to start off by saying i get a lot of attention from girls (no this is not to brag, just to give you idea of where im coming from). Im a pretty funny guy. I make them laugh all the time. Im there for them when they need help (no i do not try to be like a friend either). The problem is i have been screwed over by quite a few number of girls. I realize that those girls all have some things in common: they like attractive guys, they are boy crazy, they flirt a lot, they party a lot, etc. By getting screwed over i became not so confident in who i am. I feel like i can no longer be myself and get someone to appreciate me for who i am. Boo hoo im not crying or anything but this does bother me. Are any of you in a relationship where you are just yourself and your girlfriend appreciates you for who you are. Are you certain that your girl wont cheat on you and continue to be loyal. It just seems like most girls nowadays are a bunch of flirty sluts (not ALL of them are, but it seems like most.) What is your take on all this? Do you guys just be yourself to get the girl or do you try and be someone your not because you want that person to stay? Be honest please. We are all men here