Oh man that's a tough one. But if he hasn't been part of your life then nothing will really change for you. He doesn't deserve to be part of your life so as long as you're ok with that, keep him at a distance so you don't get sucked into the craziness.
If you have people in your life who love and care for you already, you don't need a train wreck of a man/parent to make up for anything you might feel you're missing just because they happen to be your biological parent.
I found out my bio-mom had 5 more girls and two boys after me. I only met her once the week before I turned 18. I knew about the two boys but never knew about my 5 half sisters. They found me on FB last October
I feel lucky that I never had a relationship with her given the type of person that she was. You just take care of yourself and forget about the crap-storm that others around you create for themselves.