i just found this thread and so sorry for all you and chuey have had to go through ... but one thing is for sure: YOU ARE NOT AT FAULT! if anything you have saved chuey and given a him a home and life full of love and happiness, no matter what happens in the future. i am sure he loves every moment he's spending with you and i'm sure you feel the same way.
try to keep looking up and smiling as much as you can. and the past is the past, he's with you and just do all you can now (which you already seem like you are... he's lucky to have such a wonderful mama)
have the vets found out what's wrong though? i am sending lots and lots of prayers and hugs