I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
A lease unfortunately does not automatically terminate when the parties to the lease end a relationship. As far as the apartment complex is concerned, you're both still responsible for the rent until the lease is up (at which point, you can choose to terminate and leave). You cannot change the locks, because your girlfriend has every bit as much right to be on the premises as you do.
There are a few options here:
1. Break the lease and move. If your girlfriend ALSO moves out you'll have to pay rent until a new tenant is found. If she stays, she could sue you for your share of the rent until the lease ends UNLESS the other man moves in with her, or unless she has the ability to find a roommate to help offset the costs.
2. Stay, and sue your girlfriend for her share of the rent if she leaves. If you're caring for her son, and that prevents you from bringing in a roommate to pick up her share of the rent, then she legally has to pay that money to you.
3. Stay, pay only your share of the rent, and wait for the landlord to evict you. That's going to hurt your credit, though, and won't stop the landlord from suing you for the rest of the rent due. So, in that scenario, you may still have to sue the ex.
4. Pay the $1,600 the landlord is asking for to remove your name from the lease and let you move out without further penalty.
There are some states where you'd have a right to change the locks OR move if you are a victim of domestic violence. If that is the case, let me know what state you're in and I can see if there are any additional laws that protect you.
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