Originally Posted by
lizatola 
Right now, I think I'm having trouble 'rocking the boat'. If I tell him that I will be taking ds home, he will want to know why. Then, I will end up in a discussion about how I found the red beer cup and how I fell that he was drinking while driving and then he'll deny it and get mad at me for not trusting him, etc. It will become a HUGE deal, I can already predict the words he'll say and how he'll deflect it back to me and make me feel bad for not trusting him. And, of course, I can't prove that he was drinking; that cup could have been there from a previous day or it could have been NA beer. I have no real evidence other than my suspicions and that's where I run into trouble. He will make a point of exposing the holes in my theory and that I can't prove guilt and I'll just be deeper in the mess, when I'm trying so hard to detach from it. UGH!
I FULLY understand the need to not be Mrs. Bad Guy. It influenced my actions with XAH for many years...however to put things into perspective:
Say you don't take action and your AH gets in the car drunk one day, with your son and god forbid, someone gets injured or worse...will you care about having rocked the boat then?
Please try to "play the tape all the way through" and consider the consequences of not taking action in this respect. You do not have to argue with him at all, nor explain yourself or prove that you are right, because you are LOOKING OUT FOR YOUR CHILD'S SAFETY. IMO, you can make alternate arrangements and have a stock response prepared for him when he does try to drag you into a discussion (something to the effect of "I refuse to put my son in danger").
I had to set a boundary with my XAH that also put me in the position of being Mrs. Bad Guy; I refused to go buy beer for him. I expected a sh*tstorm of retribution from him, but he just got really quiet and proceeded to act like a snotty 5 year old. Small victory for NoDay. Similarly for you, it may not be as bad as you imagine it will be...