You kind of need to get to the intimate come-to-Jesus discussion with him and ask him "what's going on..."

In other threads, we have discussed affairs and other things along with the healing that is possible. However, maybe nothing did happen. If it's truly a friend and not something, ask who she is and if you could talk to her. Nothing wrong with talking to a friend. If he protects her to the point of not allowing that, then maybe something did happen.

I'll admit - I've had an affair, been through everything from counciling to separation to reconciliation and then a few years have gone by since. It's not easy now - nothing like it was before the affair. So, do your best to try to find out what happened, if anything, and if it did, you're best bet is marriage counseling before doing anything else.