The perfect excuse for just about anyone to cheat is that they are not married. Well, once a cheater always a cheater even if you never actually perform a sexual act thoughts can be just as worst! As humans, and being a man has nothing to do with our impulses. Women as well share the same desires and thoughts as men although we tend to deny it with the fear of being less than feminine. Back to him having a girlfriend, the seriousness of the relationship can determine if you proceed but will he be upfront and honest, is the question. Is he fair game? I will say this, if you wouldn’t mind your sexual partner that you have feelings for being with another woman/man than go for it. Just remember Karma is a bitch!