Unfortunately, they have no control over it. The first step of the 12 step programme is the admit that you’re powerless and your life has become unmanageable – which it certainly has.
I feel the same as you, how you can be supportive when you’re being lied to or deceived. You’re trying to be the good person but you’re getting all the backlash from it too.
It’s a vicious cycle. Has he ever looked into getting help for this?