breaking up is something you have to do for YOURSELF. you can't think about the other person when doing it. it may sound mean or heartless but it's just something you have to keep in mind. regardless of what may happen after the breakup (him being worse off, etc), go with your gut. like everyone else said
i heard once that relationships just illuminate the problems you already have. which i believe to be true. it may sound pessimistic of a relationship but if you have a temper problem, etc already, that's going to show up in a relationship. it's -not- your fault.