To Tell or Not to Tell...

Ok... Well here is the background for this. My husband has known this guy since they were in Jr High together. They were never good friends.  Matter of fact, they only hung around each other because of mutal friends. Now, his wife is very good friends with my best friend. (Kind of strange how things come full circle)  My husband no longer hangs out with the same friends, so he doesn't really talk to this guy except when us girls plan something.

Ok, there is the background. Here is my question.

My bestfriend witnessed his wife messing around (in public) with another man while they were out of town together. It was a group of friends that went to the river for the weekend to go tubing and camping. No her husband was not there and yes, I fully believe what my friend has told me. As she began to tell me what she saw, I asked her to tell me no more. I didn't want to know who it was... what they were doing.... any details. Because I would then feel obligated to then say something to my husband, who could possibly say something to this guy.

So, I decided to tell my husband what I knew. But the real question is, we will be seeing them at my friend's birthday party tomorrow night... should we mention that we think something is a little odd or ignore it? I have gotten a few comments so far, but am curious what the concensus is.

What do you think? Tell or not to tell.