Baby momma drama

I have had problems with my fiancée's child's mother since we have been together. She is literally psycho. At this point, I'm ready to walk away. We love each other and we are having a baby together, but the thought of him dealing with her drives me crazy. I'm a rational person, but everything with her is so dramatic, violent, and crazy. I feel like if he has to talk to and deal with her, then he can just leave me and the baby alone. Thoughts?