My question involves landlord-tenant law in the State of: NJ

Hi, I've posted before but have more questions.

Scenario:
- My ex wants to move out and is demanding her security deposit.
- My landlord told me that they have to give her the security deposit when she moves out because she was the original leasee and paid the deposit. (This lease was originally signed with the prior landlord. The new landlord has continued to include both names on subsequent leases over the past ten years and never asked me for any additional sec. dep.).
- Landlord states that they will generate a new lease for me at a higher rate than we're now paying but below "fair market" value.
- A lease renewal is due in May.

Questions:
- Does the landlord have to return her security deposit if one tenant still remains in the apartment? Or, could "novation law" apply?
- Does removing one name from the lease entitle the landlord to generate a newly negotiated lease at a higher rate than would normally be allowed by town ordiannces had both names remained on the lease?
- Do I need to involve a lawyer?
- What can I say to my landlord?

I have tried to reach my local board of rent leveling, to no avail.

I would be so grateful for any help regarding my rights in this matter. Thanks.