I am so sorry that you are in this situation. Feeling angry and upset is not the best emotional situation to be in to negotiate with her.

As Sky noted, if your name is on the lease, it is legally your home, and there is not a thing that your roomie can do to force you to leave before the move-out date.

The next step is to decide what is best for you. Do you want to continue living with a couple who do not want you there? Do you want them to leave, and you will find new roommates? Do you prefer to move? Is there a way to negotiate all three of you living there? Those seem to be the basic choices, and you are going to have to get used to one of them.

You also need to find out if she has signed an independent lease with the landlady starting in September. If your roommate has done that behind your back, then you are going to have to move out. You also can approach the landlord, sign a lease on your own, and start looking for roommates.

I agree that your roommate ethically owes you financial help to find a new place, if that's what she wants you to do and you agree that is the best choice for you. However, an ethical obligation is not the same as a legal obligation.

You might point out that she owes you whatever part of the expenses you would pay if you move out sooner rather than later, as well as a refund of your security deposit, but I really don't see how you can get her to pay more than that if she simply doesn't want to do so.

Again, Lady M, I am sorry that this is happening to you.