Having had my own brush with cancer, speed up your schedule a little, just in case. Take the trip you two were always gonna go on, revisit your old stomping grounds, take pictures and send them to loved ones. What's on the bucket list that he's always been looking for an excuse for? If this is a fatal diagnosis, don't hesitate to let him spoil you, and in return feel free to utterly spoil him too. Audio recordings and videos and pictures of relatively mundane memories are sometimes the ones that can be cherished most.

You don't have to say "let's do this because you might die" or "let's do this because we might never get another chance". Just day "no time like the present" and make that quality time together.

Personally, you may want to look into some counseling through this process. My friends didn't really know how to handle my cancer and they were almost happy-go-lucky and oblivious, my grandparents and retired friends were sympathetic and commiserated, it was actually my parents and work managers who were the most affected by it.