I think it's great you brought him home and are nursing him back to health! :) He is a really nice looking Betta and I'm glad you're giving him a chance. He hung in there long enough for you to help him, so it proves he is a fighter.
I didn't see if you were soaking his pellets before he got them, I don't know if it would help, but if he is still pretty weak he might be able to eat them easier? I don't know if this would help though.
He is so skinny.. My heart goes out to him, and to you