I think the key here will be your letter. That will help him to tie it all together with the sentiments that underlie what you are leaving for him. I personally think he needs to read that while you care for him, still love him and hope things can be worked out, you cannot under any circumstances agree to become the abuser's latest victim.
I think the books are a good idea. But again - tie it all together in your letter. Let him know that solutions are possible and you have even provided him with some of the most important literature he can read. Now it's all up to him. What does he want from life?
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)