How do I get my grandpa to communicate better with me? I have battled his diabetes, afib, etc., but he won’t discuss anything with me when he is feeling ill.

Do you mean your Grandfather speaking to you, alerting you when he is feeling unwell? So you can get help?

Does he recognise when he is unwell? People can be vauge, sluggish or unaware when diabethes is not well controlled or oxygen levels are low.

Is this what you mean?

Are you your grandfather’s primary caregiver?

Is it new for your grandfather to be the "strong silent type"?
Can you identify a reason for his non-communication?
Does he seem very exhausted for depressed to you, or are you seeing this as more or less an overall weakening of a gentleman who is ill and exhausted?

How old is your grandfather?
Are you his caregiver and do you live with him, or he with you?

More information may allow us to make better guesses but I am thinking it is ONLY a guess, and you may know him better than we do, and thus be able to make better guesses at why he is more quiet at present.

Without Grandpa's permission, his docs cannot give you any info, but you can give them info. Let his PCP know if he seems to be feeling ill and that grandpa won't tell you anything. Tell as much as you can of symptoms and ask doc what they can do to get appropriate care for him. Can they order a home nurse visit? What else can they do? You need the professionals to step in.