Hate to throw this into the mix but is there any possibility that this incident with your BF's BF, did not really happen and that your BF made it up to "even the score" with his ex-wife? His behavior towards his BF is not consistent with you two doing the dirty 100 yards from him, he would also not be so forgiving of you either. Something does not add up which you may wish to investigate further. That being said, I too have blackouts. These things are very dangerous and can degenerate the brain capacity and increase memory loss which no one wants.
Our reality, we just have to stop drinking. Keep access to this site close to you and reach for it everytime you want a drink. Tell you boyfriend he has to support you on this journey and just fight for your own freedom. You cannot stop your boyfriend or friends from drinking but you can stop yourself. Offer to be the designated driver or decline invitations until you are in control. It's hard, but the best things in life are worth fighting for.