My best friend from college. It was a toxic and emotionally abusive friendship. He isolated me from my friends and family, telling me they weren't good enough or smart enough for me to waste my time on, and once I had no one else but him he decided I wasn't good enough or smart enough for him. He had no one else though so he would stoop to "teach" me to be better. The most minor infractions would piss him off and I would spend a whole evening trying to atone for "texting something with the wrong intonation" or whatever he was mad about.
Sometimes he would decide I wasn't worth it and end our friendship, but he would always change his mind because he had driven everyone else out of his life too (shocking, I know). One day I hit my breaking point and realized I was relieved rather than heart broken when he told me things were over. He later magnanimously offered to talk things over and I told him no thanks.
It took me a long time to get back to a healthy place. Honestly, I still hear the scars of it. Every year he would contact me and ask to talk, and I would tell him no, that I didn't want him in my life. Several years after the last time I saw him in person, he contacted me again asking for help. His relationship with his boyfriend was on the rocks and no one knew him like I did, so could I please give him some advice. I'm at a different place in my life and feel that I'm strong enough to offer help to someone while still taking care of myself first, so I told him I would help him but it would only be one conversation, and then we go our separate ways. He flew off the handle, saying that I must not care at all to offer so little. I sent him a journal entry I had written (a therapeutic exercise I had done for myself a year earlier) outlining the years of twisted emotional abuse and after effects I had struggled with because of him and told him to fuck off. I finally blocked him from every form of communication (his previous messages had always been pretty sporadic and I would always think each one would be the last). It's amazing how much one person can fuck up your head.