Louise,
It is treatable - this site is excellent in what the treatments look like. As far as supporting him, do it as a friend. Tread very lightly on his turf with his wife. I am running into a situation with my husband where his "ex" even though they never married, has tried to infiltrate herself onto caring for my husband and it has caused problems. She has does some very, very mean things to try to sway him to her in which he has acknowledged, but it still has caused him pain and frustration, whereas they are going thru enough - caregiver and patient. Read this site as it has a wealth of knowledge and support.

Good Luck!
Paula