The problem with basing a character on someone you know

In my soon to be released book, there's a character named Trevor. Trevor is not one of the main characters, but he is important to the story, and he's based on my ex-boyfriend. A long time ago I dated a guy who treated me so badly that I knew I wouldn't get over it unless I did something. I started writing a story with a character based on him. This is the only character that I have ever written based on someone I know in real life, and I don't plan to write about anyone else that I know. I also told the ex that I was writing about him, and he didn't seem to have a problem with it. He said he wasn't going to read it, even though at that time we were in a "good" place again, but he said it was cool. I stopped during a small frame of time when he was back in my life. I guess I couldn't write a character based on someone when I had fresh emotions towards them. I started writing about zombies, and didn't look at this story again until I got stuck on the zombie story. When I looked at this story again, I realized that this story was good! It was the kind of story that I would like to read, so I started working on it again. I edited what I already had, and then started adding new parts. I realized when I edited it the second time that the story was too personal. There were things I'd written about that I would have been horrified to release to the world. I had to really look at Trevor's character and fictionalize it more than I had. I had to think about his motives and come up with a reason for him to want to hurt his ex-girlfriend. I also had to alter their past relationship so that it no longer mirrored the one I had. I had to think about my own ex-boyfriend and wonder if he would have done the same things that Trevor did. Thinking about my ex while writing this was the worst part. You think about all the pain you endured because of that relationship. What I thought was a way to get rid of my pain actually ended up causing me a little bit more pain. I think it would be different if I was writing a character based on a friend, but I would still have to think about that friend in terms of motive and how they would behave. I think it's actually harder to write about someone you know, instead of someone you've made up. I don't regret including a character based on someone I know, but I don't foresee myself doing it again.