How to handle it when you feel guilty about the way you treated a deceased person?

So about six months ago my grandfather died suddenly. Routine surgery when very bad. At the time I was mainly shocked. I felt absolutely no sadness and regretfully relief. See I was not close to my grandfather. When I was little I was, I mean most kids find their grandparents to be the best people in the world. But as I got older I started to see who he truly was. He was a cocky, snobbish man who cared about money and appearances. He showered my sister and I in expensive gifts in the hope of buying our love. I started to see how badly he treated others and my moms parents. He was just overall not the greatest person. So when he died, I wasn’t upset and while my parents and sister were crying and grieving, I went on with my life as usual. I did cry at the funeral but it was more do to the guilt at not feeling any sadness and just overwhelmed. I’d never been at the center of a funeral, the closest person I’d lost before that was my second cousin. So all of the people saying sorry and all the pictures of me and him freaked me out. But once the funeral was over, I didn’t cry again. Haven’t cried since and haven’t really thought about it. Yesterday though was Christmas so we went to the place where we’d scattered his ashes. My parents and sister were crying and I just sat their, literally just enjoying being outside. When we left felt sick with myself for not feeling sad! I feel like something is wrong with me and I don’t know what to do.