Why does my partner change around his friends? Watch
Surely if he loves you he would not put you through this.
Excessive drinking and taking drugs is not good.
In my opinion you need to sit down and have a long meaningful chat with him, tell him how you feel and what it is doing to you.
If he has anything about him and thinks the world of you he will take it on board and change.
And find someone with the integrity to not cheat on you under any circumstances and someone that has the self discipline to not go into slumps for days.
IE free yourself to go find a normal well adjusted man. There are enough of them about.
Sounds like he needs to grow up, find some better friends and stop bowing to peer pressure
If he's cheated on you and you dislike his behaviour then why are you still with him?