daberry,
I have been battling depression for most of my life and I am around the same as your son. Obviously everyone handles their depression differently, but maybe I could help shed some light

A little over 6 months ago, I put myself in a similar situation as your son...posting a message on facebook about how depressed i was and illuding to the fact of suicide. I honestly had no intentions of offing myself, I think I did it just for a reaction, to know that someone cared. About 30 minutes after my post which came at about 3am, i got a knock on the door and it was the police. We talked for a few moments i assured them that i was not going to harm myself. I took the message down and spoke with my family to reassure them i wasnt going to cause myself any harm. In doing so I caused them great worry and they called a crisis team to come talk to me. I was not happy about meeting with these people at all, i didnt think i needed it. a few months later i was in a dark place and expressed feelings of not wanting to live. Enter the crisis team again...and again i was not happy to see them. I did not lash out, i met with them to apease them and to get them out of my hair asap. I dont know if your son has been in therapy before? I have had a couple tries at it and the last therapist started to make some headway...I started to discover that a lot of my issues where from childhood. please understand that i came from a very loving household and was never abused or anything like that as a child. I had two wonderful parents who love me very much, sadly almost to a fault. I do love them and always will, but as i am going thru therapy again there is a bit of resentment towards them. But i know that as i heal, so will the relationship with them. The hardest part for me is that they had no idea that they were causing this sort of emotional damage...and why would they? They loved me unconditionally, whats the harm in that?
Its obvious that you love your son very much and you are willing to do what ever it takes to get him help, that hardest part is that even though we may know we need help, we dont want to admit it to ourselves. Making that call to a therapist isnt the easiest thing to do. Even when i admitted i needed help, i had someone else make the call for me, just knowing that i wouldnt have done it.
Its understandable why your son is upset, but you didnt do anything wrong, you did what a loving parent would do. He made the situation worse by acting out, is he still in the mental health facility? As for why is he "punishing" you this way, well only he could answer that. But as the saying goes, you always hurt the ones you love. He could be acting out towards you because he knows you will keep trying and keep showing him more affection. Which would feed his ego, but it also gives him a sense of control, he knows that if he lashes out, he has some type of control over you.
As I said before, each person handles this disease differently and this is just my two cents. As for any suggestions I would continue to stand by him. Is there someone that he is close to that he would listen to with out lashing out? If there is, id approach them about possibly talking with him about getting into therapy. He will just meet you with resistance and angst.
I wish you both the best!
IC