Rumor that my (29f) partner (29m) is having an affair at work

It come to my attention that a rumor is going around at my partners work that he is having an affair with a coworker. I found out because I saw a message from a coworker asking if everything was OK. I asked what happened and that’s when he told me. Apparently it’s been going on for a week. My partner didn’t tell me about the rumor at first because he didn’t want to make mountains out of mole hills.

I was aware of his friendship with the coworker who is involved. My partner has always assured me they are friends and he is not attracted to her because shes not his type. I have tried to be supportive of their friendship but deep down I never liked the fact they were friends. He never tried to hide her from me and I have met her once before.

Part of me does believe its just a rumor as the people he works with sound immature and they like to link people up with eachother. He told me the coworkers are making fun saying things like “when are you going to leave your partner for xyz coworker” and “what’s going on with you and xyz coworker.. huh?”

My partner apparently told them to stop because he is in a commited relationship and feels what they are saying is uncalled for.

I dont know if I am being irrational but a small part of me worries something did happen and now they are both stressed that it’s coming to surface and are trying to cover it up. I guess time will tell.

Not sure what to do?

Tldr – there’s a rumor circulating at my partners work that he had an affair with his coworker.