Wow, that's a whole lotta questions...
Well I hope the guys and gals here can help flesh this out and give you some more specific advice, but I just wanted to focus on one specific part of your post. You asked,
"What is the key to getting to the point in the movie where he realizes he can feel again, is it the release of the grief or the feeling wanted without strings attached or feeling useful and needed?"
To be honest, there is no magic key that will work for every person. The only thing we as friends, lovers, and fellow brothers can do for anyone making the journey to healing is to work to provide for them the safest enviornment within which they can discover for themselves just what they need. No one person's story of abuse will be the same as another's, and as such, no one person's specific path to healing will mirror another's.
The most helpful thing you can do is to take him at his word, and let him tell you what he needs. Sometimes his response will be silence, or maybe even he'll push you away. You have to respect that and not push him. If you find that that his behavior causes you much grief and anguish, that's ok, and it may be a sign that you need to give some space and time to things. As we've said, what is most important is that you make sure you take care of yourself first. Someone who cannot swim has no business trying to save someone who is drowning.
"I am not a mechanism, an assembly of various sections.
And it is not because the mechanism is working wrongly, that I am ill.
I am ill because of wounds to the soul, to the deep emotional self...."
Healing D.H. Lawrence