im sorry OP, but i'm a woman, and if i truly cared/loved the person i was with, i wouldn't put myself in flirtatious situations like that. and she does it continuously since you said she talks to him often. this girl knows what this guy is about and she likes the attention. who wouldn't. but if they were just "friends", she would have told him flat out that she doesn't feel comfortable talking like that because she is with someone. if he was her "friend", he would respect that and stop talking to her like that. this flirtation is continuing because she still has feelings for him. maybe she can't act on them now, because he's however many states away and she's in a relationship with you, but she's keeping her options open by not shutting him down. you need to address this and tell her your concerns...stop brushing it off and making it sound like it's no big deal because it is a big deal. she's being completely disrespectful talking to a guy like that when she's in a relationship with you.