Read and reread FeelingGreat's post just above. Follow that to the letter.
I would not tell him ahead of time, I would make a plan and be gone when he comes home. Leave a note or send a text after it's done.
He WILL try everything to get you back. That's what they do. "I promise this time will be different. I'll get help. I can't live without you. You can't live without me. I'm going to kill myself. I understand now, I'll change. You're the only one I've ever loved...etc...."
Alcoholics are Master Manipulators.
Get out. You've already decided. Cut your losses and go ASAP. Forget the money he owes you - don't worry about him and his issues. Worry about you and why you feel you deserve to be treated so badly.