Legal Question in Real Estate Law in California

Re: Rental

First, keep in mind that there are two separate contracts here: (1) the lease, which is between the two of you and the landlord; and (2) the agreement between your girlfriend and you to share an apartment.

I'd start by carefully reading #1, the agreement with the landlord (the lease) to see if it says anything regarding the permissible number of adult occupants (a 19-yr. old is an adult). If the lease limits the number of occupants to the two of you, you are breaching the lease regardless of any (#2) agreement between you.

If the lease does not prohibit the son's residency there as a long-term guest or family member, then we have to look at agreement #2. You probably didn't have any written agreement between you; that would be unusual between a boyfriend and girlfriend, although that would have been a good idea. It's possible, however, that you arrived at some kind of unwritten understanding about use of the apartment or the kid's presence that could be upheld as part of an oral agreement. Unless you could plead and prove such an oral agreement exists, your girlfriend probably has the right, as a cotenant, to allow the son to move in.

As for paying the landlord to cancel the remaining term of the lease, you'd have to pay the full amount demanded.