What's the real reason why guys act different after you've done something with them?

ewe met and we clicked instantly, things were good and we finally ended up getting close (but nothing serious) after it all went down, he won't call me back & when he finally does, i don't have any wants to pick up--i guess everyone's right telling me to kick em' to the curb and find a GREATER MAN who will treat me good because goodness i ******' deserve that ****. it's a shame he's a player and has girls lined up and they're all after him--i can't blame him for having game like that--but for him to show interest in me but fake it just for me to be another girl on his side? that's extremely foul! so, if there's a genius out there, pleaseeeee tell me why do you guys act like that after we do something good to you? it's almost as if you guys compete to see who gets the most girls and you suck because there's already one who's good for you, if you'd just open your eyes--i would have treated you so good and you're blind to realize that JERK! WHAT'S A GIRL TO DO ABOUT ALL OF THIS? HELP!