I am absolutely not an expert and in no way qualified to tell you what to do, but from the outside I see your best course of actions as....

1 - run....run far away from this destructive person and go to where your friends are and tell them all about this.

2 - Go see a therapist who can help you move on with your life. It's normal to be sad when you lose someone but it's also normal to be happy after they leave. I'm starting to see that myself.

3 - I suggest reading a book called "No More Mr. Nice Guy" and see if you recognize these behaviours in yourself. If you do, it can help you become a happier person who seeks healthy people, not broken people who need fixing.

Again I'm just some random dude on the internet, talk to some friends about what to do next.