I'm gonna go out on a limb here and suggest that the affair with the OW predated bomb drop number 1. Yup. Maybe it was a different OW, but in my experience, most guys don't drop the bomb UNTIL they have slept with or at least engaged with heavy flirtation with a new affair partner.
My guess is they fought, or she backed off, or he felt guilty, but after the period of reconciliation with you, she reeled him back in.
He's still depressed/in MLC and like a drug addict, has fallen off the wagon again because of the great high that you get from infatuation.
Let me make one suggestion - when he returns from his trip, announce that you are going out of town for a few days. Yup. He can watch the kids and the house. You're taking a break, a mini-vacay all of your own.
Be a little vague about it. You're going with "a friend". Or you're going off alone "to think about what you want". Don't let him know where you're staying.
If you can afford it, get out of town. Visit a friend, or go to a spa, go lay by a pool and have drinks with umbrellas in them and read novels - whatever.
If you can't afford it, go crash on a friend's couch and watch Netflix. Just get out of the situation for a couple of days and let HIM wonder about where you are and what you're doing.
See - as long as he knows you are there waiting as his plan B, he thinks he can enjoy his affair and still be able to come back to you when he's tired of it. But the minute he starts to think it's possible that YOU might go out on the town and pick up some guy in a bar, or have a secret lover like he does - well, suddenly that affair of his may not look like such a good deal.
Mind you, I'm not suggesting you lie, or actually meet any men, or ANYTHING like that. I'm just suggesting that you leave a little bit to the imagination, let him wonder a little bit. Be independent and a little bit mysterious. If he's wondering about you he won't be thinking about her..
