Cowboy needs an angel

Cowboy, my best and most loyal friend, was a very sick puppy when I adopted him from the Humane Society and I was not told of any of it. He died a few times in the first week after bringing him home and the vet thought he'd need to be put down. I never left his side and miraculously he survived the night. The vet told me it was purely me and my love for him and vice verse that brought him through. She was in shock that he didn't die. He has now started having seizures again amongst other things and I am terrified that it may be starting all over. I can not afford all the tests, blood work, meds., vet stays, etc. that he is going to need and I can NOT handle the thought of losing him, since I have lost my entire family, without putting forth 100% effort into saving him. Please help my best friend who has been the only one there for me when I lost everyone. It will kill me, with me health, if I lose him too.