Deposit doesnt get returned till the property is vacated and broom clean and penalties for damages or late rents are deducted.
You need to talk with the boyfriend, see if he plans on renewing lease on his own or vacating. If staying he needs to pony up what she is owed, and sign a new lease with his name only. If leaving you can settle after they turn the property back over to you
You hold on to the entire deposit until the lease is terminated. The boy friend is responsible for refunding the girl friends portion of the DP. Not your problem.
When he leaves you return the full DP to him less any damage deductions.
And when writting the check for the returned deposit I would write the check to both of them. John Doe & Jane Smith so they both have to endorse to cash!
The existing lease needs to be terminated before any deposit is returned.
Talk to the bf and see if he is willing to sign a new lease with just him on it, same rent, for however many months left in current lease. He’ll have to pay the full deposit (he already paid half, so he’ll have to pay the other half) and then the place is ‘his’.
Then sign that new lease, and have both bf and ex-gf sign a lease termination ending the lease early.
THEN the deposit can go back to her since she is no longer on any active lease and you have a full deposit from the current tenant.
If they are both listed on the lease you can't split the deposit. She can request her fair share of the deposit from roommate and you can do an addendum to release her from the lease but you need to hold the entire lease until you regain possession of the property from all tenants.