Trusting is right--detaching is really what you need to do here. In fact, I want you to pretend you're an outsider and go back and read your post. What would you advise ME if I were the author of that piece? My guess is that you're going to see some things here that are SO not about you.
That being said, I have a different thought on the trying with OW issue... just remember that "try" in his vocabulary means something totally different than "try" with you. "Try" with you means put forth an extreme effort to heal individual and marital hurts with the common goal of working on the R. "Try" with her means that he will try to minimize collateral damage as much as possible because he's pretty sure that his failures with you and her AND your kids are going to mean exposure to him. BTW, exposure is going to mean that everyone knows he's failing at everything he's doing.
Cagz, I know it's hard to attempt to find sympathy for him. But looking at him spiraling out of control as an outsider, I see him as someone desperate to grab a rope. He's not going to climb out of that hole on his own until the ropes stop being thrown to him. It's going to be very difficult for him to do this... and it's also going to be painful to watch him hit rock bottom.
You're not responsible for this mess or throwing him a life line. Saving himself is an inside job. You have a hard enough time taking care of yourself and your kids. So my free advice is to don a new set of glasses and take a look over at his train wreck. You weren't the cause of it, so you're not responsible for the solution. HE is.
One more thought. Your S19 is a man. Let him manage his own R with his dad. If he's going to choose to heal, it's going to be a factor in motivating him. While you don that new pair of glasses, maybe try and see S19's R with him from his eyes: he's screwed up royally, his son has expressed disapproval and boundaries that never existed before, and he can't seem to stop flunking out with everyone. Hell, he even lost his job as the icing on the cake. When one feels like a loser and is mentally ill (depression IS a form of mental illness), he's not going to be inclined to deal with S19 until he's figured out what the heck he's doing. Now take those glasses off and put ones on that permit you to see your own life clearly.
Leave him be, sweetie. I KNOW his actions have put you in a precarious spot. I'd be lying if I told you that it's not going to get harder with his job situation. I understand the fear on your part. But fear isn't going to solve the problem and neither is your STBXH. The only part of this equation you can control is how you deal with your own set of problems. Put on a pair of blinders and stop looking at his train wreck.
Detaching is the ONLY thing that will get you over the hurdle. After you can do this, you'll be in a better place to determine what kind of R you can have with him post-D. But you'll have to do more detaching first. Walk before you run...
You can't force friendship with someone who doesn't want it. So let sleeping dogs lie for now and just take care of yourself and your kids. That's all God asks of you. Let HIM worry about your H, okay? That job is bigger than you and it's not yours.
Hugs,
Betsey
"There are only 2 ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."
Betsey