This is terrible!
Actually, you don't need to accept this situation or forgive him at all. You can kick him out, change the locks, and file divorce papers.
And then you can find a Dom who will treat you with love and respect.
I cannot say it better than Meera.
Your spouse cheated and wants to use the D/s dynamic to just make it ok? No... not ethical, dude. Not ethical poly, not ethical D/s. Just cheating crap.
A dom only GETS to be a dom to the sub because of the sub's desire/wishes and consent. You both play in the D/s framework you both co-create. Unless you signed up for this treatment (and your response indicates you did NOT) he's crossing lines. If he cannot control himself how can he hope to control you in a good D/s dynamic?
Could call shenanigans and just end it. You don't need this. Say no thanks, not participating! Not good for my health! Do what you gotta -- change locks, get std testing, get counseling -- do your self care you decide you need to heal YOU.
Hang in there!