You sound like you're doing pretty well there Solo. It's a rollercoaster, there will be good days and bad and you just have to dig deep during the bad ones and wait for better ones to come along.
I was thinking about you having sex with him when he's sleeping with an OW. I'm sure the sex is tempting as a way to feel connected with him, but he is definitely using you. Maybe it'll be easier for you to say no to him if you imagine him having sex with you whilst fantasising about her? How much of a turnoff would THAT be for you? It makes my skin crawl just thinking about it.
My kids are similar ages, 14 and 17. It really [censored] the way a H can abandon his kids like that, I feel like my H will never be respected by our kids for having done that. No matter how much he bleats about wanting to be happy, his behaviour has been selfish and actually pretty unforgivable. My kids never asked him to run away, they didn't deserve this. I didn't either, but at least I know where my faults lay within our marriage, our children are innocent in all of this.