If you've said how you feel, I think it is OK to stay away and let him take charge of his own recovery.
He has not been honest with you pretty much from Day 1 so you have no obligation here.
If he is "offended" that's pretty much his problem from where I sit.
You're right, you didn't sign up for this and quite frankly you don't even know who this
person is sober.
I'm sorry this happened--what a shock.