I have the same with my daughter, first it was for one year then she began speaking to us again then I offended her again, I forget what I said, and she didn't speak to me again for four years. She has lovely children and now she has stopped us seeing them & they live a 3 hr drive away so we don't bump into them.
She has started speaking to me (by phone) again recently because she wanted some family information, but its hard to feel relaxed and enjoy the long phone chats we used to,
I'm the same as you, I just accept it now it is really hard to talk to someone like that as you say, you just always worry about saying the wrong thing.
I think she expects me to plead with her to start speaking to her again and I don't, I just don't want to as I have no idea what to say or not say to avoid a repeat performance. I think she has no idea that she has damaged my relationship with her, she's so bound up in how tough life is for her and how I have added to that stress. My feelings for her are the same as with her siblings I love them all the same, but I don't have the energy for the drama anymore, so I feel like you, at peace.
I sent her a really nice bottle of perfume for Christmas, for which she thanked me by text, & offered to give £10 for each child xmas (which is what I do for all my grandchildren) but she didn't take up my offer as she didn't give me her bank account details.
Perhaps the nice part of your son will come back, I do think its hard to change entirely, completely all in one go cos you can't easily shake off the old bits of you that easily without support, but realisation might sneak back one day.
