Hmmmn does he make it known (in a respectful manner) that he's taken? As much as it is annoying for partners, a little flirty banter is bound to happen occasionally between all sorts of people. I do think it is disrespectful for people to consciously try to tempt or seduce (even in small ways) people who are in a relationship. It reminds me of a vulture circling.

I do have this problem, too, with one of my SO's good friends. I'm getting much better about keeping my jealousy in check (especially after discussions with him to clear any misunderstandings up), but I do still find her really grating. She's actually not always a very nice person, in general, and even though I have tried to make an immense effort to bite my tongue and let any nasty barbs from her turn into water and roll off my back...she just has a special way of trying to drive a wedge between he and I or say something to put me down that wouldn't necessarily be readily apparent to him (very Mean Girls, you know).

He can't control her behaviour (though, he can have a talk with her about it and see if that helps). However, my suggestion would be to talk to him about it a little more and see if anything in his behaviour can help you feel more confident about your bond or discourage her from flirting with him and encourage her to support your coupledom. Of course, you don't want to go on a jealous tirade (I've done it and it doesn't really help matters so much), but you have every right to discuss and improve your relationship with him. I have learned that when I am upset about something G has done (enough to want to talk to my bf about it), I give a specific example of what happened, how it made me feel, what efforts I had made to correct the situation, why her behaviour was destructive to our relationship, and even suggested ways that he could help.

How do you know she is hitting on him? Is it a FB thing or does he tell you she is? Either way is not good. What does he say to her when he gets hit upon?

lunar--thanks i will try talking to him
eternity-she says things like shes not worth your time jono you can do better then she turns around and insults me on his fb comments and she is someone he works with and it pisses me off.hes stood up for me but still she crossed the line a couple times.