First you are a great man for rescuing Rex, Don't be to down on yourself because you gave him a 2nd chance in the first place.The best thing is your the last thing he saw before he passed which is a great thing. I know it's very hard i had to do it before and i'm dreading when it happens again, Sometimes another dog is the best healing. I know i didn't want another one right away but my women talked me into it, so i went and rescued a dog and it was the best thing i did. You will find a new Buddy. R.I.P. rex.