Would a girl that likes another guy but is in a relationship do it to anyone?

Ok I know this girl that likes me but she is in a relationship with a different guy. They have been together for a year. We met 2 years ago before she knew this guy and we always had a crush. She lives very far away from me( a few states away) and at the time we liked eachother we could never do anything about it because we lived so far away. Now I can travel and see her, But she has a bf and I don't think she likes him because they have had a lot of hard times and he has cheated on her. she knows its wrong to like me but be in a relationship with someone else. She says she cant control who she likes and that when we have held hands and been close she has felt very guilty. I think that she is in a relationship that isn't worth it, but My question is If I were this girls boyfriend(of course I would treat her right like a princess) would she do the same to me? Would she like someone else while we go out and flirt and hold hands and kiss them on the cheek? Or does she do it because she really doesn't like her boyfriend but is attached to the relationship? Thanks!