Make sure you don't lose touch with him at all costs. He maybe unhappy where he is and no doubt want to be with you now but as long as you can still spend time with him and share part of his life he'll still know you are doing your best and the love will be there regardless of his words.
It's the price you have to pay for your misfortune. Sorry, but there's not much you can say. You can love him a lot though, that might help.
time effort and patience. at one stage i severely doubted me and my mum would speak again but we got there.
Oh and parental alienation syndrome sucks. sorry for you there
hold him hug him and hope for the best
maybe he'll better understand as he gets older.