Legal Question in Real Estate Law in California

Put your personal safety first! If you are dead, your estate will still be liable for the rent.

Hopefully, both of you are "on the lease," and if you move out, your roommate will still be on the hook to the landlord for 100% of the rent. He will, of course, have a counterclaim against you for your portion, but you'd probably have defenses if you've been threatened.

There are other possibilities such as restraining orders, but if the roommate is truly dangerous I would not rely on a piece of paper so much as putting some physical spece between the two of you.

In a suitable case, you should also report the details to the police. Don't put your life in danger over a mere matter of rent.