If a chick cheats on you, or breaks up and then starts seeing people immediatly after -- they're full of shit and nothing more than confused, psychotic, girls; Not even women.

Seriously, as everyone stated; Move on. Quit being "there for her" and quit being her whipping boy who's around whenever she has time for you.

Go out and get a new girl -- not to be serious with, but to date and fuck.