here are my thoughts, mentally:
you are in the "one more chance" stage. curious how long he has been back in the house. if my guy was away for months or even weeks, wild horses would have to keep me from being in the same bed with him, whether i had an early wake up call or not.
you have some intuition for a reason. all too often we don't listen to what it is telling us, although i do realize that sometimes it goes haywire because of broken trust.
but don't minimize what you are sensing. you know him.
imo if he is not working a strong program, he has no chance of being sober. he can knock off the booze for awhile, but he will be white-knuckling it. which is probably what he's been doing, which is probably why, if your hunch was right, he wanted to stay at the friend's and induldge.
is he doing aa or a different program?
this thing about checking up on him. for one thing, if we continually are checking up, it is exhausting and it makes us crazy, plus takes away from what we should really be doing.
but!
if this set-up occurs again, i say it would maybe be worth it to do what you were thinking about. and it's because it would put all of this to a stop. at least then you'd know what you now suspect, you could follow through with terminating the marriage and put this all behind you. otherwise it can just drag on and on and on and that too is unhealthy.