Dear OP. I'm sorry you're in this terribly hurtful situation. But there is a way in which you can sabotage his weekend, bring about some peace of mind for yourself (even if this involves facing further emotional pain in the medium-term) and retain your dignity, all in one fell swoop.
Tell him you know where he's going, and that if he does, the marriage is over and his bags will be waiting for him on his return. And mean it categorically. Follow through on it, and have his belongings packed and waiting when he comes back.
There are all manner of possible outcomes from this. One is that it will certainly ruin his tryst if he has to spend most of it on the phone looking for alternative accommodation. Two is that the thrill of an illicit fling and the prospect of actually living with someone are two entirely different things. A short sharp shock might bring that home to him and make him fully aware of what he's doing. Both he and OW have to want to come to the decision to leave their spouses and be together, and very often the reality isn't that simple.
If he really has emotionally checked out of your marriage and is set on leaving, it will happen anyway and there's nothing you can do to stop it. You may as well know the truth and start to deal with it now. It will hurt, but death by a thousand cuts (playing the painful game of trying to catch him out or sabotaging his time with OW), will end up hurting more. But following through with this will likely force his hand one way or the other, and knowing he has to find a new place to live when he comes home should take the gloss off his weekend a bit!
Finally, remember that the best revenge is to live well. If you hold onto your dignity you'll feel so much better in the long-run. For your own future happiness, you need to accept that if one person in a marriage decides it's over then it's over, and it's probably best to let them go.
for you.