Hi Anne, I am really sorry for what had happen with you. You are doing a great Job by keeping in touch with his parents.
It is really very clear from your writing that you really loved your man. Now think in this angle, if he could still see you from somewhere, will he like to see you living in pain of guilt all the time. By doing so you are bringing pain to his soul. Check out this story. It might help

http://upsohigh.com/nurturing-the-jackfruit/

No one can go back and undo things but we can take right steps now and make things better in future. You have doing a great thing by still being in contact with his family.
Family was the one thing about which he cared. The other thing he cared about was you, you should take care of yourself as well. Free yourself of all your guilt and try to live a life which he has ever dreamed you to live…