I am writing this as the wife of someone who died recently.

Writing from my experience I would say let him tell you , or not,in his own time how he feels .

Both my husband and I never spoke about the fact that he may not survive this aggressive cancer he had , but spoke about the future .,holidays we would take, but probably we both knew we never would.

Be guided by him and his attitude, that’s how you can help him.Let him be in charge of his feelings , and as you sound  close to him you will know how to respond 

Ihope this helps in some small way 

Hello, I'm the wife of a husband who has lung cancer and agree with Lancashire lass.  We never discuss death or his incurable cancer, just live each day as it comes.  So follow his lead and try to be normal with him, that's what they want, normality   I know this is going to be hard but just let him know you will be str for the family.  Carol