Klutz,
You have had such a hard childhood. Remember - your dad's behavior and addiction were under the control of alcohol. You were close and sad witness to it, and some of the sadness and despair over the memories comes from a lingering feeling that one could have done something. You were a kid.
Unfortunately we are often attracted to addicts. You have to remember that your fiance's addiction is beyond your control. You can be open to talking to him about the addiction - make it clear that it hurts you but that it is his choice. Your own sanity is at stake, and your child's welfare. I am not suggesting you leave him but you need to establish boundaries. You can, repeat can, control your life. But you can't control others. I pray you will find a way out of the shambles. And I get a sense that you will.