I have decided to let my boyfriend move into my house/room. I don't get along with my three roommates we use to be good friends and back then we talked about if my boyfriend moved in we would split the rent up. Since we aren't on good terms and I never come out of my room unless to use the bathroom or make food I didn't think it would be fair to split the rent up. So me and my boyfriend decided we would split my room rent and then we would split our utilities evenly 5 ways. The roommates said that wasn't fair and he wasn't allowed to move in. Is there any law about him moving in? Should he sign the lease or not?

FirsT is this a rental property? Who is on the lease and what does the lease say about additional occupants. Also what state are you in?

This is a rental its in Ca. Right now Im on the lease and so is my roommate Mason my other roommates Jimmy and Danielle and suppose to sign the lease and they actually have it right now, but they are threatening to move out instead which is fine by me because they have already paid there last months rent and security deposit.

Oh and the lease doesn't say anything about how many people live there.

If the lease doesn't deal with it, then the roommates have to decide among themselves how to divvy up the expenses.

I don't know about the law, but I do agree with your roomates that your proposal is not fair. If you BF moves in you should split the rent and utilities 5 ways. Remember that your rent covers more than just your room - there are also the common living areas (bathroom, kitchen, etc) which your BF will be using, as well as the other common areas of the building whose costs are being paid by the renters (elevator, parking lot, etc).