Move out!

He is not capable of being in a relationship or being honest as long as drugs are in his life.
Do both him and you a favor. Leave.

Staying means you will enable his ability to continue his behavior, after all he got away with it once, so why should he change. going back means you accept his behavior.

If you leave he may wake up go get treatment or he may not but he is the only one who can decide to fix his life. You can not fix him nor are you responsible for him.