Ok, so the facts as I understand it are;
Your bf and your mate had some same sex activities while alcohol was involved. Your mate was married at the time, and now his wife has found out and is understandably upset. Am i right so far?
Assuming I'm right, there are too many factors missing to get a clear picture of why you are asking if he is fooling himself. Does he deny having any same sex attractions (SSA)? If so, what were the circumstances that he was asked or confronted? And then the real question is why you are concerned (asked in a sincere manner)?
First off, let me explain a bit of why I think I can give some advice. I have been a closeted bi for many, many years. I too had some same sex relations while I was with my GF, and she found out. She was understandably devastated. Up until then, I didn't even want to admit it to myself, but was forced to once I was discovered. Now here's a big one for you to consider,,, if someone had tried to force me to come out, I would have put a large distance between me and that person. Not that the person would not have been trying to help me do what was best, but because I was not ready. This will most likely happen if you try and pressure your mate into facing his SSA before he is ready himself. The best that you can do is to just let him know that you and/or your bf (he might feel a little more comfortable since he has "been" with him) are there as a friend should he need to talk. Here's another fact that might be hard for you and the bf to understand, since he is not out and is dealing with a wife he may not (more than likely "will not") be able to relate to you as an openly proud gay man/couple, but there are several support groups for Mixed Orientation Marriages/Relationships (MOM's or MOR's). There is also a very good "women only" group for the wives/SO's of an MOM/MOR. If there is a way, please let him know this. Once I know that they will be passed on, I will give you the links to them. My GF and I are involved in a few. We are also very, very close friends with a couple in England who are also, so there is support near by. If as I suspect, he is uncomfortable talking about it, slip the information to him in a short letter.
Just please don't try and force him to face and accept it because "you" think it's best. Just as a matter of opinion, I also think it would be the best for him, but HE has to decide that for himself.
Good Luck,
p.s. this board moves so fast that I would request that you PM me if he, they want links to these groups.