We have been together for about 2 years now and are engaged. We've broken up before because he tried guilting me into having sex when I wasn't comfortable with it. We got back together, but unfortunately it is only after getting engaged that I realized he never changed. He is mentally unstable and I learned that last time we broke up he used dangerous amounts of alcohol to cope. I want to break up with him, but I don't want him to start drinking again, or worse, kill himself. What do I do?