Sadly, I was in your position a few years ago, I really didnt know what to do and could have done with books or info as written by the sufferer.
All I could do was concentrate on offering practical help whenever I could When my BF was in hospital, I sent a card or notelet every day. But it was so difficult to find the right thing to do or say.
A couple of mutual friends and I used to discuss things together then take it in turn to keep up a sort of support system,and their support was vital for me.
But there is no easy answer.
Love to you and your friend.