I'm so sorry you're having a tough time!
About the apartment- I would not pay another penny to that woman. She is definitely taking advantage of the situation and I'm wondering if she will ever do what she says she will.
When I lived in Boston I broke many leases. It is actually a really common problem there because almost everyone needs at least one roomate. Not intentionally, just things came up! Roomates moved in and out-- and rents became too high (3 bedroom apts could easily go for 4500 a month) and I have never been taken to small claims court for what I've owed on the lease.
Plus from what you've said it seems that it would be a health violation to even be staying there in the condition that it is in, so I think you would have that fact backing you up.
About seeing someone for your depression... I truly think you should. I see someone weekly for my anxiety/depression and it has helped me so much. I am not able to be on medications because the ones that I were on caused some major weight gain (although they tell me that's unusual). But, I know many people that took the same drug I did without that side effect and it definitely helped with depression.
I really hope all this levels out for you and you can relax and enjoy yourself! I think anyone in the same position would be stressed out, I know that I would!
