To break up or not?

So my gf and I have been together for four years. The first year was a complete disaster. She was hooked on pills, cheated on me many times, was violent (called the cops once), and completely unstable. We broke up, but I took her back (maybe not the best decision). Since then, we've been pretty good, not great though. We've since relocated to a town 500 miles from our hometown, where we don't know anybody. She likes moving frequently. I don't. I have a very secure career, and she bounces from job to job. I pay most of the bills, (rent, groceries, etc) and she picks up the small things like internet and cable. I do make more than her, but she has the ability to make more at her job but does not try to. Our sex life was great for the first 3 years of our relationship, but of course now it's very boring. I know part of our lack of a sex life is because she has gained a lot of weight, and I am not as attracted to her as I once was. I'm sure that sounds shallow, and it happens to most people, but it's the truth. We're both around 30 years old. She had a hysterectomy at age 26, which is fine because at the time we both agreed we did not want children. Now, she regularly says she'd like to adopt. I'm still not sure. She also presses the getting married 'issue' often. I'm not sure I even want to get married. I fear if I were to break up with her, she would do something terrible, like suicide. I'm just torn. I don't know if I should tell her all this and break up with her, just express my feelings and try to work it out, wait and see if it gets better, or not say anything and break up anyway. This is only my 2nd serious relationship at age 32. So I am just lost really. Any advice would be great. Thankk you.