Roommate Drama 🙄

Here's the story: I have lived with my roommate, Emily, for 2 years. We go to school together, we hang out, we make food together- we do everything together, she's my best friend.
Emily's boyfriend lives in Florida (thousands of miles away), he came to visit once and ended up staying for nearly 2 months. I do not like this guy, he's a bum, he's verbally abusive, he's unkind... I could go on. I just think she deserves better and I definitely don't enjoy him being here for so long.
In November, Emily found out she's pregnant and, naturally, wants Baby's father to move here to be with her. Makes sense. But our lease isn't up until July and she insists that he moves in next month.
I get it. She needs to live with him, she needs support from her baby's father. But I do not want this guy to move in with us. He's already lived with us once for 2 months, I can't handle living with him again, and this time longer.
We're trying to break the lease, but it's proving to be more expensive than expected. It sounds like Emily and boyfriend have made up their minds and he's definitely moving here next month. I guess I could move and the lease would fall on her (boyfriend is a bum and has no money), but she's pissed that I don't want to live here with her and her boyfriend and I think the idea of me moving and the lease being on her makes her even more mad.
I don't really know what to do. I can't live with this guy for several months again, but I also don't want to ruin this friendship. Am I being overly dramatic for not wanting him to move in? How do we make this situation fair? Is it wrong for me to move out when he gets here and expect her to finish out the lease or pay to break it?
** Boyfriend didn't pay rent the last 2 months he lived here and as far as I know, he wont be paying rent when he moves in next month.