What do i do?

I am living with a girl I used to work with. I found out recently that she had put off paying the councill tax and we had been summond to court. she hid this from me and was only that a rang to check something I found out. I now have the option to move...

back to my mums (closer to work and cheaper much cheaper) How do I tell her I want to move and should I move?

Well, I think you pretty much said it in the question. Be very direct, don't be accusitory, but don't back down from your position. I used to live in NY, but not NYC, so I am not familiar with counsel tax. Esp if she hid it from you, you have a definite reason to get out of that situation. I have been with a roommate who didn't pay his rent before. I came home to an eviction notice... yeah pretty upset.

Larger questions would be about voiding any lease, or what to do about possible communal property you have. Also you may need to look into common law. I don't know if NY is a common law state or not, but some common law states have a Ridiculously short time in order for common law to go into effect.