hmm... I think that drinking buddies and FOM (friends of marriage) can be two different categories.
I think that many people are in denial about being alcoholics and they do not realize how much better their lives would be if they could get sober once and for all.
So many people think that they can 'control' their drinking and/or still drink socially or switch to beer or wine from hard liquor and that will do the trick.
Unfortunately, they usually find out that they are wrong and the toxic, alcoholic thinking and drinking takes over again.
That's where continuing to hang out with former drinking buddies does not work.
I've said it before...but IMHO after infidelity all the rules change.
In my house that meant that anything that got him into the mess of the affair had to change.
No facebook friends, no going out with 'the guys', no more secrets, transparency in all passwords, cell phone usage, you name it.
And most of all - no more drinking or drugs-ever.
That part of his life was over.
And he would be the first to tell you that he loves his new life.
Now...as for FOM....I would consider someone that knew about the affair and encouraged the affair or helped the WS get involved in the affair as someone who was NOT a friend of my marriage and someone I would not want in my life.
However....just knowing about the affair and not telling you may not mean that the person was in favor of the affair or did not support your marriage.
Ironically, right before my d-day I found out about a very close friend's affair and her d-day.
I knew all the details. And I did not contact her husband.
I was a good friend of his also but because I had no experience with infidelity I did not know how to react.
I did not encourage my friend, instead I did warn her and discourage her behavior.
But...my reaction was nowhere near as extreme as it would be today after experiencing the pain of d-day myself.
Infidelity is one of those things that until you experience it yourself you really do not understand it at all.
My friend's husband has continued to give me the cold shoulder ever since.
I was a friend of their marriage and was rooting for their marriage to survive.
Unfortunately, my girlfriend did not go that route.
So...I just wanted to give that insight.
Not sure if your situation is similar or not.