We can’t change the past, sad as it is, but the outlook for the future doesn’t look good. I dont really know what to do about this, I’ve tried confronting him with facts but there was just no effect. And continuing to engage with him hurts me so I’m kinda done with that.

Unfortunately the only way to reach people like this is to listen to them and expose them to another viewpoint but without challenging their beliefs. It's a skill that can be learned, but also it requires a lot of emotional bandwidth and it is absolutely emotional labor. You have every right to be done with him and no obligation to help him out, but if you do want to learn more about how exactly you can persuade someone out of being brainwashed I'd recommend the following three books (in that order) for some perspective and thoughts on the matter: