Maybe you could write him a very short, very friendly email and tell him that because of all of the stress, you will need your space. That you can't write him because his son has been so bad to you, you have to be safe, and you can't be safe if dad knows where you are or who you are around?

I dunno. Maybe just say you care about him, but you are working on yourself.

This is so frigging hard. I am sorry, Nikko.