Shutting him out is how you handle an addict. You refuse them any support, practical, financial, emotional, etc...
You can get family to intervene and confront him, but you are too emotionally involved and vulnerable to be doing that yourself.
Once you expose the affair and people start turning their heads away from him etc the pressure is on... You have to let him wrestle with the life he's created for himself until he chooses to exit that to safety or he drowns there...
