Ok this is seroius ..why do some girls cheat on there boyfreinds?

Girls cheat just like guys. Sometimes it's self esteem, & sometimes it's wishful thinking that he might give her more of what she thinks she wants. If she's cheating [mentally, physically, or openly flirting], with other men at all, you're just a stepping stone or a safety net until something better comes along. I would take a step back & decide how serious you are about her because it sounds like you're gonna get hurt. That always makes it hard on any future girls you see and can ruin any real love you may find by comparing all prospects to her.