I am sorry to hear this, but hope for the best! You said he may have it, so..maybe he doesn't? Reassure your fiance that all hope isn't lost, and be there to talk to him if he needs it?
It's never hard when you find out someone you love may have a serious illness, but some times things happen. When those bad things do happen, all you can do is hope and pray for the best. Be there with those people, and help them through it. Maybe you can let your fiance know that you are there, and encourage him to help his father through the rough times.
I'm sorry that this is happening to your fiance, though. I wish you the best.
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well-behaved women rarely make history.♥