Scooby, You can't control your h and if he wants a divorce, he'll get one whether you like it or not. Some of them think that by getting a divorce it will make things better for them. I can tell you that they are all in for a rude awakening when it comes down to the amount of money, time, paperwork, etc., that is spent on getting a divorce.
In their minds, they think that after the divorce everyone can be friends...unfortunately, it doesn't always work out that way.
Some will say they want a divorce when they feel like they are backed into a corner. Others mean it and will follow through very quickly and others will drag their feet. The best thing to do is listen and observe. He may not do it, but we don't know which way he'll go.
No, it's not odd that he wanted to return to you when his girlfriend was w/her boyfriend. Some do this cake eating waffling back and forth. Had he returned, the minute she was free, he would have been right back into her arms. They like to keep us on the back burner in case things don't turn out the way they think that they should.
You need to stop drinking his Kool-Aid. He loves to project on to you about abandonment. If you had abandoned him a decade ago, then why has he stayed so long? He's going to say or sorts of things to pin the blame on you. Don't drink that Kool-Aid. He's miserable and doesn't want to look within to find the real reasons for his misery. You didn't break him, therefore, you can't fix him.
Nothing you say or do will make him change his mind during his crisis and that's why it's important for you to focus on yourself and your children. Stop focusing on the ow. She's taking up head space and not paying rent.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.