[Usernames Suck]

You need to leave. He doesn't sound like a good person at all if he cheated on his wife with you to begin with and is now trying to control you. Making you feel like you'll be killed if you leave is NOT ok. Blackmailing you into staying with him by threatening to kill himself is NOT ok. That's emotional abuse, pure and simple, and it's good that you've figured out that this relationship is unhealthy.

I recommend that you try to seek out some help. If you have any friends or family you can turn to, tell them about your situation and ask them for help. If there are support groups in your area dedicated to helping people in abusive relationships, or any hotlines, do that as well.

I don't know how old you are or what your living arrangement is. If you're still in school, talking to a teacher about it could help as they may be able to give you advice and keep you safe. If you're under 18 then the adults in your life should absolutely protect you from him so there's that too.

No matter how old you are, if you fear for your own safety you could try to seek out legal help also. I don't know what that's like in your area, but depending on what the local attitude to this sort of thing is, you may be given any protection you may need so he can't stalk you or hurt you. Any local groups, charities or hotlines will be able to give you more advice about this. And definitely alert people you trust to what's going on. These things can help keep you safe, they may be able to offer you a place to stay if you've been living with him, and they may be able to help by doing things like not leaving you alone if you're afraid he'll find you and hurt you.

Even if you want to help him, it'll be easier for everyone if you are safe, and this may also help him get the help he needs. Your safety comes first.