I agree with many of the others. I think it sounds like you're doing a ton here to try to make things work and I think honestly that a fair amount of this is normal 17 year old behavior that is exacerbated by the sitch. I watched my youngest sister act very much in this way after me and her other 2 siblings were very "easy" to deal with for my parents. She acted much like your son is acting and yet, there was no divorce, no familial problems that were pressing at the time. It was just her personality. For the record, that sister is now the very closest to both my parents and the total opposite in personality. She is constantly driving to see them and spend time with them and the most thoughtful and loving towards them of all 4 of us. So I just think a fair amount of this is normal angsty teen. He just has a way to focus the behavior with there being a family problem going on.
With that said, I also agree to DB him. You have often said DBing is really a way of life, so, it would follow that you use that here. The more you push him, the more he'll pull away. My mom used to tell my sister when she was in her "phase" that she loved her all the time--and yet prior to that mom wasn't an "I love you" kind of mom. My sister just resented that attention, to be honest. She'd only roll her eyes. Not saying you shouldn't tell him you love him, but you dont' want to be pushy I guess.
M45 Bomb 6/09; EA 6/10; Divorced 1/11 Proud single mom of 7 little feline girls and one little feline boy "Fall down 53 times. Get up 54." -- Zen saying