I'm just getting here, so I apologize if I'm going over old ground...
Have you tried setting him free? Sending him a "Protection Letter", and having all communication about S5 done through a third party?
Encouraging him to rejoin the M doesn't seem to be working, and it's making you miserable. You're right; let him feel the consequences of his actions. Remove yourself from his life for a while so he can see that you aren't the cause of his unhappiness.
Between your H's addictions to OW, drugs and online RPG's, suing for full custody seems like the right thing to do. You don't want your child in that environment, and he is definitely not acting like a fit parent right now.
