Hey Jeff,
Please, please, please don't do this to yourself. You were a friend and counselor when he needed you. You aren't responsible for a person's decisions about life and death. It's only natural to want to do everything in your power to help him, and I would bet that if it we're possible to ask him, he would readily agree that you did more than enough.
Regardless of what religious faith one may have, one of my favorite phrases is "Having done all, I stand." Right now you should be standing tall. You did everything you could for him.