I hear NC being banded a lot in your thread and I just wanted to say it is d@mn hard emotionally and physically to maintain a NC position when you have to interact with someone, much more so when you are in the same physical space. It's doable when they live elsewhere. It's doable when you don't have children. But it isn't so easy when you are in the same space.
May, the beauty of you is that you are so full of compassion and empathy. You care. Don't let his whims turn you into an empty vessel spouting yes and no answers with a soul-less voice. I don't mean you should return to being his sounding board. His best friend is gone. He needs to feel that. Actions not words.
Him: "May - I'm feeling confused" You: "I'm sorry you feel that way. I hope you can work through whatever it is that is happening".
Him: "You're not the same person" You": "I am sorry I come through that way. It is not my intention".
Him: "You're a blah blah blah" You" "I will not listen to this"
Then leave it at that.
In the meantime, turn that compassion and empathy inwards. You have a huge heart. Do not let him turn it into stone. It is time to start learning some self-love.
If he talks about moving out/moving to another room, just simply let it be. He wants a reaction (begging/pleading/negotiating/long drawn out conversations). Don't give him one. If he is reading self-help books, then let him. It has nothing to do with you.
You do you. Warm, compassionate, intelligent, beautiful you.