You do not need to know details about any affair at any time. You should not let that affect your settlement in any way. Don't let him off easy hoping to preserve some "friendship" and don't try to punish him for his behavior.
This is a financial arrangement. It needs to be equitable, a reasonable situation for both parties. If you can stay in the house until D16 graduates, that's good. By the time you guys finally get things rolling, it won't be for much more than a year after D is final.
Don't worry about changing your "verbal agreement." Everyone knows that a verbal agreement isn't worth the paper its written on. In this case he pressured you to accept what he thought was reasonable, having never laid out what all the assets and liabilities are. I'll bet you that there is stuff he has--an extra account, some stocks, something--that you still don't know about and won't know unless your lawyer files for discovery.
