Afraid My Fiancé Might Have A Thing For The Guys She Works With

Hi there, I’m married to a man in the military but engaged to someone else. Don’t judge me, it’s complicated. Anyway, my fiancé recently started working at this new place and she’s been acting weird around some of the guys who work there too. Last night we were talking about her job and how they go out for drinks after work. She got really quiet when I mentioned one guy in particular, his name is Mike, he’s older than her. Now I don’t think anything has happened but she seems nervous whenever I bring it up or ask questions. Is this normal? Should I be worried about them having an affair just because they’re close friends?