XH and I had separated (but temporarily and so that he could get clean and sober - nothing else had worked - and have a last ditch attempt to properly work on things). During that time, I worked on finding him help (again) to get clean and sober (again), worked FT, got counselling for myself, parented the kids and kept the house ticking along. I thought he was doing what he could to get sorted. Unbeknownst to me, he was already with OW. His ex BF then found out, didn't agree with what he was doing, refused to be a party to it and gave him an ultimatum to tell me himself, or he'd tell me. Anyway, XH didn't tell me so XH's ex BF told me (which let me keep my faith that there are decent guys out there!). I filed for divorce (XH made it very clear that OW was the One who understood him and supported him better than I ever could/did*). XH and OW move in together and treat me/the kids like shit. I had to involve the police and my solicitor as XH was so nasty.
[* I was the breadwinner. He didn't work due to an injury from an RTA. I also did the majority of housework, mental load, life admin etc etc. I supported him a LOT! This was to enable him to rehab and get back on track. He didn't: he got an alcohol and drug addiction and all the counselling/private rehab/you name it didn't help. I think he basically thought that whatever he did, I would forgive. But I had my limits, told him my boundaries and he just ignored them]
Four months later....they split up in an absolute train wreck blaze of glory. And it WAS glorious. The stupid cow OW (she WAS one of my friends) basically messaged me expecting sympathy when they split that evening. Apparently XH had slept with OW's sister. Anyway all hell broke loose, and I just sat back, watched the messages pinging and laughed (an awful lot). I told her that she could keep him, and maybe share him with her sister. Also told her a few home truths (she knew I was married to him and she knew our situation). I don't think I'd laughed so much as I did that weekend.
A week or two later, the crawling back started. He actually doesn't think that divorce is such a good idea after all (too late, papers signed and sent to court), he thinks that I should consider it all before I continue with divorce (too late, already did that!), that actually he does love me and he didn't mean what he said. ----> what he meant was that I wasn't so bad after all, that he's living in a van at the place he has a lock up/rented a garage, and that living back home with me and the kids is actually a nicer prospect. I told him where to go.
Even 2/3yrs on, my XH STILL laments the fact that he didn't want a divorce/I divorced him when he didn't want a divorce, blah blah boo hoo. The strange thing is that he had a very funny way of showing that when he fucked off with OW instead of actually getting his shit in order and working on our marriage (which he had fucked over with all his previous shitty behaviour). Him buggering off with OW told me that he didn't consider me/the marriage even worth trying to fix.
My thoughts OP? He had an OW, or a potential one, and that went to shit. Even if no OW was on the horizon, if things were that shitty, why the hell didn't he communicate that with you, and look into counselling/seeing how it can be fixed? Why did he just fuck off without so much as a by your leave? Did he really think you were that disposable, that he could just bugger off and then suddenly come back as if nothing happened? I'd tell him to take a hike.