Are you sure or just suspect that your husband has some feelings

for his co-worker?

I know I would not be able to keep it just to myself, and pretend nothing is happening. I would speak out my suspicion, my concern and point out that it would negatively impact the marriage.

Depends on your personality, do you normally share what's on your mind or keep it within. It's hard not to build up resentment if you have doubts about him. Ask him what if you start to flirt with other people?

Anyway, it's very touch. So I hope it's just your suspicion and your hu*****and is in fact totally devoted to you.