My boyfriend gave me an ultimatum that I don't think I can follow. What do I do?

For two years I have been battling this evil cat of his. After the cat attacked me and everyone else in the face, he still chose to keep the cat. I don't feel safe with this cat, even the vet said there was something wrong with this cat. It is dangerous and acts ferel. I have compromised with him by allowing him to keep the cat as long as it goes in the room when I go home. I don't feel safe with this cat ramdomly attacking. It is my right to not have this animal trying to rip out my eyes or slice any other part of my body. Last might he told me that I have two months to get over my fear of having the cat in the room with me or he would leave me. I am so hurt and I love him so much, so this is hard for me. I am sad and crying my self to sleep at night because of this. I don't know if I can have to courage to do what he wants. I would forever live in fear as long as the cat lives. I can't believe he would choose this dangerous animal over the safety and well being of myself and others. If I tell him no, I have no doubt he wouldn't even blink an eye about leaving, as long as he has his precious kitty. That is all he wants. I tried talking to him and he wont budge. This hurts so bad and I don't know if I can get over him if he leaves. We have been together for almost five years and I have grown to love his family very much. I love his nieces so much, as I have watch them grow up. This is so painfull. How do I deal with this?