Married GF flirting with co-worker?

We are into an extra maritial affair, she is married. Now she tells me there is this guy in office who flirts with her. She says she is "distracted" but im sure she is flirting back and enjoying every bit. Now im having a real tought time here digesting all of this and it is hurting me like anything. It was bad enough dealing with a husband in the picture and now there is this co-worker!!! The co-worker is married himelf and has a kid but which guy wouldnt mind a good time if the girl is willing. Im afraid things could go out of control and I might end up loosing her if I dont do something about it soon. I really dont know how to react, what should I do? Really hurting now...