Him getting "over" on you is certainly an option. And really there is no way to know for sure this is not the case.
It comes back to is this a "fair trade" for you. Is what you loose worth what you may gain... even if you gain nothing.
I am not exactly sure how much of a "loss" we are talking about.. but if it is less than 50k.. it is likely worth it. If it is more then that.. we may have to talk.
6 months should be fair.. that would be 24 sessions? I suspect you will get a quick idea of where things are headed after the first consistent month. Maybe include that if he "misses" a session or 2 that kills the deal.
In the long run.. make a deal.. you both can live with.
As far as OW.. you have to suspect that with as much time has passed.. he has not been "faithful" and has likely created other "relationships". I am just gonna say.. if that was a deal breaker.. we would not be trying to do what we are right now.
This situation.. is a Hot Mess.. no doubt. Still just make smart choices that you can live with down the road.
If you do that.. you win.. even if you are "moneyless".
Relax Eat Think Act normal React.. Smartly. Do something different. Emulate. Do Work.