He's telling you he sleeps in the same bed with another woman, a woman he left you to be with... and he doesn't have sex with her??? 
He must think you just fell off the turnip truck and bumped your head. Grown men don't leave their wives, their home, everything they've accumulated just to move in with a coworker and not have sex. The fact that he "went dark" on you when she got home tells you plainly that she doesn't know he's communicating with you, so you can safely assume that he's still acting like he wants to be there. Don't you think she'd be a bit suspicious if her boyfriend was having a literal panic attack every time she wanted sex? Wouldn't the cat pretty much be out of the bag at that point?
I think he is realizing how hard life is without me (I make 4x his income), and me taking care of him. He even said last night “I think she is just playing house. She doesn’t know how to take care of me the way you do."
You are NOT his mommy. It's not your job to 'take care of him'. And given the fact that you make 4x the income, I'd be getting with my attorney to strike while the iron is hot and he's living with someone to see if I could mitigate alimony expenses. I'll be frank with you... it sounds like the new car smell has worn off the OW to some degree and maybe he's not quite as comfortable as he was while you were seeing to his every need. But this isn't the first time he's cheated on you. He's cheated before and there is ZERO indication that if you take him back now he won't do it again.
I'm in R myself, and 'yes' I do believe it's possible for people to change. But my WH worked his ass off to stop me from divorcing him. When he put out feelers to see if it was possible, he backed it up with immediate action. He changed jobs, we moved, he sold his cars (triggers), took me on vacations, and treated me like a girlfriend he badly wanted to impress. He ghosted the OW, changed phone numbers, deleted emails, and handed over passwords. He'll hand me his phone 5 times a day if I ask. Are you seeing ANY of that?
And what about you? Let's say, he dumps the OW and becomes a model fWH... there's STILL all the trauma to process. There's still putting yourself back together. We don't heal just because they come back. We still have to figure out what we really want and rediscover our own independent identity.
I'm not trying to talk you into taking a position on R or D, but you did ask... and this guy's not making a good enough offer IMHO. He's not even being candid with you yet.
