I'm devoting most of my "thought time" to him
This is more destructive than anyone can imagine until they have been there, probably more destructive than we realize even when we're doing it.
You don't have to let him go, but you have to give yourself some mental space, even if that means pushing him out of the front of your mind for a while. Honestly, whether you're spending 3 or 13 hours a day thinking about him and only him, the only one feeling the effects of those hours of thought is YOU.
I'm so sorry all of this is happening to you right now. It seems his family is out of the question, but is there anyone else, a mutual friend or a counselor, who could give you an outlet for all of this? You sound pretty overwhelmed.