Pancreatic cancer is a very, very hard diagnosis to hear for a loved one. I don't think he's dealing with you in manner guided by rationale rather than an emotionally guided state.

Give him some time. Don't hound him with texts, but don't ease off too much. Just text him every now and again, asking things like how he and his mother are doing. Things like that. I think in time he'll come around.

Take care, and I hope things work out for you.