Why boys are the one who fool girls?

ok. i am 21 and single. use to have a bf. he didn dump me or anything. its dat i heard frm lot of frds and people dat there is the boy who alwaz use girl or say fool her. even if they have very caring wife or gf they juz find a mistress. wads wrong guys??? i think u all should avoid looking at other girls once u have one. u knw how hard its for da girl when u go with other. i have no experience but i can tell as i saw my friend crying. and eventhough i don't know about her bf i hate whoever he is. i saw the pain in her eyes. very bad. just tell me whats your problem boys??