How to help my fiancé while his dad is dying of cancer as I am also close with his dad.

I have always been terrible with death. I cry and I cry even if I’m not close with the person but know someone close to them. I was 5 the first time someone I knew died. It was my great grandma. I wasn’t close with her but I cried so much because I knew “grandmas not gonna have a mommy”. Sometimes I’m so empathetic it’s a little too much. My fiancé says I am there for him and that he’s so happy to have me through this. However it feels like I’m not doing good enough. Because I myself am so heartbroken. I love his dad. We go to his house every week and that’s always the highlight of my week. (Before the hospitalization and diagnosis of cancer). I thought we had so much time left I could wait to make him a grandfather after the wedding. He always chatted with me about this. I feel so selfish for crying and sometimes my fiancé’s ends up comforting me. And I absolutely feel like crap when he does. My fiancé’s only 26 going through this and I’m only 19. We never imagined having to go through this so early. This wasn’t expected. Thanks for those who have read! I know it lengthy!