It's my mother's partner. He's been around for a long time but he's a bastard. For a long time after he and my mother got together, he behaved in very sleazy ways towards me behind her back. I was an adult but I was too scared to say anything because I didn't know if my mother would believe me. With hindsight, he was very manipulative about it (e.g. I tried to arrange it so I was never alone with him, but he went to my mother and complained about being hurt that her kids never wanted to spend time with him unless she was around too). Everyone else in my family thinks he's a great guy. He's done some other shitty stuff (going a few years back, he pretty much harassed his female boss because they had a dispute over sick leave, e.g. slitting her tyres and gaslighting her by hiding her stuff, but my mother has always played it down).
Anyway, I don't want anything bad to happen to him because I don't want my other family members to be sad. And it's way too late in the day for me to make any big revelations. But I'm worried that, if something bad happens to him, this will be the end of my relationship with my DM, because I'm not going to be able to fake the level of sadness and grief that she'll want from me. I'll do anything in practical terms to make things less difficult for her, but I'm a shitty actress.