My father, who convinced me (16 m) at the time to move in with him instead of my mother when they moved. All 3 of the other siblings stayed with my mother. He then kicked me out the week I turned 18, a week into my senior year. Since then he stays in touch only to speak with his grandchildren (now going on 4 kids). I have never been anything but opportunistic and positive in our interactions. Regardless he still acts like I am a burden to talk too. Am now 37, and finally getting to the point I should accept it. I'm the complete opposite with my own children and can't comprehend how someone could treat their child like this. How do I cope? It eats at me. I will answer any questions in depth if it will help in understanding the situation.
I will agree with most that professional support is needed. For me... I had to realize that I could not change people interact with but I could change how I reacted... Not ideal. I'm sorry you're dealing with this.
Phase 1: Can't change people. Phase 2: Can control how I react (to diminish the harm I feel). Phase 3: I feel less harmed, but my reaction shouldn't further enable their shitty behavior. Phase 4: See ya! And I'm skipping phases 2 and 3 from now on.