G is for Grandpa

Ex's grandfather developed Alzheimer's disease at a fairly early age. Ex, being the Negative Nancy that he was, firmly believed that he, too, would get Alzheimer's.

Then Ex's mother started showing signs of dementia. Ex immediately decided that this confirmed his belief that he would die of the disease and he gave up. Ex stopped making plans for the future. Anytime anything in the future was mentioned, he would make a biting remark about how at least one of us would be around to enjoy it.
                             
Finally, I was too drained by his negativity to even be scared of him anymore. The last time he told me he was getting Alzheimer's, I calmly told him that it was a possibility that it would ruin the end of his life. Then I told him that, by worrying about it and obsessing over it constantly, Ex was letting it ruin his entire life. Even though he didn't have Alzheimer's, he was dying of it.
                          
Amazingly enough, Ex heard me. That was the last time he mentioned it. His mood seemed to lift and brighten a bit. Although brighter than pitch black is still pretty dark.