Confusing deposit refund situation! Help!

[Robyn Joy]

As a tenant and someone looking into having investment properties down the line, I have a particular situation I need advice on.

I was renting a flat in LA with a friend, both our names were on the lease. She planned to move out when the lease was up, as did I. A week before we were meant to give notice to the landlord, she changed her mind and decided she wanted her boyfriend to move in with her.

The landlord told me that since the unit would not be fully vacated, despite him making her and her boyfriend sign an entirely new lease and pay him a large deposit (partially due to him being a British citizen, supposedly), that I would have to recoup my deposit directly from her. She agreed to this, but did exactly what I expected, which has been dodging me since April. 

My question is, is the landlord in the right to force me to recoup my deposit from the other tenants, even after making them sign a new lease and pay him a deposit? My legal obligation was up, and yet I'm stuck trying to get money from someone and I'm unsure of my legal rights to pursue them.

California law says a landlord has 21 days to pay back a deposit minus itemized cleaning/repair fees otherwise they may be subject to twice the amount of the security deposit in statutory damages in addition to actual damages. Would this apply to recouping from the roommate and her boyfriend?

I'm afraid of running out of time due to any statute of limitations on taking this to court, which I really do not want to have to do.

ADVICE BADLY NEEDED!