Why do some girls do this? girls why do some girls do these??

Ook lets say a girl cheated on her boyfriend they’ve been going out for 4 months now and the boyfriend is very sweet I mean this guy would call her from day in and day out she very lovely dovey! Tell her how much he loves her would even even write poems for her even send her cards etc... and he’s very faithful he and even likes to even joke around as well as with a great personality and he prays for her since he’s very reglious etc… and the girl cheated on him 5 months later they don’t talk that much on the phone like they use too in the beginning and since they don’t talk that much she sum times accuses him of talking to other girls even though she talks to other guys or a guy in particular! And that guy that got cheated on hasn’t don’t anything bad or anything for her to cheat on him would it be hard for her to find a sweet guy with a great personality and shell get eventually cheated on by the new guy and why do girls always do this dumb stuff sumtimes not all girls though???