I'm a 21 year-old male who, despite being (what I think) handsome, confident, and overall fucking awesome, has a massive curse that has left me brutally cynical when it comes to relationships and intimacy.
Every person I have ever been in a relationship with- every single one- has cheated on me or left me for another person. Not just left me or broke things off with me; left me for another person. Not a single exception. Seriously, all 4 break-ups I have experienced in my young life has ended with "I'm sorry... but... I've found someone else" (except in 1 exception, where I only found out 2 weeks after the fact that she was boinkin' a good friend of mine).
First off, what the hell do you expect from having fuckbuddy relationships? That's how they work, stop crying about those.
However, as for regular relationships, I feel for you. I'd say by far the most likely reason is that you've just had bad luck. I mean, come on, it's presumptuous to think that you have some sort of mental control that works so well that EVERY girl you date will be FORCED into cheating on you or falling in love with another man!
Being clingy, needy, and submissive are the fastest way to drive a girl away. All 4 of those girls left you because they lost interest in you, or because they're attention whore psycho bitches you shouldn't be dating in the first place.
Ironically it's the conquerable ones which are probably more suited to long-term relationships.
Yeah, where the women make the rules and keep the man on a tight leash. If you want to be your girlfriend's or wife's stooge, fine. I'll be hitting the town with my friends for pool and drinking while you cuddle up next to her to watch American Idol.
Not American Idol, but the cuddling thing is good enough for me.