I hate that feeling Nick, when you find out something about someone you like/love that you're not sure if you're meant to know, but you can't talk to them about it but nor can you just forget about it...it makes next time you meet them very difficult. I really don't know what to suggest, other than to possibly not think too much about your grandpa's past actions, but to think about how he acts now, and how he treats the people around him now. I mean...we've all done things in the past that we aren't proud of right? I'm not saying your Grandpa was right but...I dunno, maybe thinking about that might make being around him now easier? Good Luck anyway, and take care.