if I am 17 years old and my mother keeps threatening to kick me out of the house can I legally leave.?
What state are you in?
In general, no, your mother (or legal guardian) is legally required to provide for you. Now, if mom says to leave and does not care where you go, then you can leave. But, the minute she wants you back, you will generally have to return or you - and the people that are helping you - can face the possibility of criminal charges.
So, why don't you come back with the state you are in. Also, where is your father in all of this? Does mom have sole legal and physical custody?