Ready to leave... But when?

This is huge... After almost 6 years, 2 of marriage, I have finally decided in my heart that I need to leave. I'm leaning towards legal separation for now.. See if he changes MAYBE we will reconnect, but who knows. Anyways I am in a predicament. He knows I have wanted to leave for a while. But then I changed my mind and we went to counseling and I've stayed, now I have made my decision to be thoroughly done, though I won't be able to physically leave him until 6 months from now, until I finish my accounting degree.. Do I tell him my feelings now and then it might be wierd between us for the next 6 months, or pretend everything is ok until I'm done with school and can move away? 


Also as I sit and type this I am thinking about me telling him I'm going to leave, and I kind of feel sorry and bad for him.... WHY???!!! Ugh the manipulator that he is will make me feel like a horrible person for leaving.... Please tell me it's ok to leave, I've been through enough and I can't take it anymore!!