Stuff; unimportant

I see people all around me getting loved, being in happy relationships, doing things with friends.  People talk to me in school and at least pretend to enjoy my company.  I don’t understand why every time I try to make a move on a girl, they stop talking to me for at least 3 months and every time I try to make plans with ‘friends’, they’re always doing something.  Everyone who supported me, ever, found other people, boyfriends, other things, better ways to spend their time and it seems a chore for them to talk to me.  Am I really that undesirable?  Is everyone else really better than me?  Am I just ridiculously unlucky?  Or do I just not understand how humanity works?  I don’t understand why all this is.  And thats the worst part, it kills me not to know the reasons behind things.  If I understood, I’d be fine with it.