Forgive me if this comes across harshly, I haven't posted here in years and the time and distance from my own sitch have allowed me to let go of the emotions.
It sounds like you kept recent communications strictly business and as soon as he added something personal you reciprocated. This gave him what he wanted, knowing that you are still there for him to meet his needs.
This is the time when you should be focused on YOUR needs. Put him aside entirely. Communicate politely about business (money, kids, house) but nothing personal. It's not your job to protect him from the consequences of his actions. It's not your responsibility to manage his relationship with your grown children. You've done that for decades and look where it got you.
You should spend your time and energy figuring out what you want the rest of your life to look like. Including and especially if and why you want to continue in this marriage that you describe as unfulfilling. No one is going to put you first except you so do that. You deserve it.
If you love somebody, set them free. http://tinyurl.com/2empx2g
