Why not to take advantage.... to me it sounds she and the boyfriend are no angels. I feel bad every time I turn down a chance to fuck. Everytime I swear to be faithful I feel testosterone escaping my body.
You both suck....she's trash for cheating on her boyfriend and you're trash for knowingly being "the other man"...the way he treats her is none of your business and does NOT excuse the cheating....apparently the way he treats her doesnt bother her much if the stupid bitch is still with him....
Let's just put it this way....would you have wanted your friend to do that to your girlfriend that you thought you were going to marry? Probably not. Both of you were in the wrong. Everyone has hormones, if I screwed a guy everytime I thought he was hot, I wouldn't be married right now.