daring, I'm so sorry for what you had to deal with. At least you laid all of your financial concerns out on the table and I'm glad you pointed out what you've been paying, etc. You've shouldered a huge burden and continue to do so and here he is only doing a small helping w/a small portion of the debt. Gosh, the man is one lucky duck because of that.
You have every right to have a good cry. The man is clueless and you have done everything to try to make things comfortable for him. Your h and S17 will have to work out their relationship on their own. As for your younger son, he will need some counseling to help him work through his concerns and anxiety issues (if they are there).
Please take care of yourself.
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.