06/22/2011 at 11:00 AM EDT
In his new song, "A Better Place," Glen Campbell sings, "I need the ones I love Lord/More and more each day."
The lyric is more personal than the world knows: In an exclusive interview with PEOPLE, Campbell, 75, and his wife, Kim, reveal that the singer
has Alzheimer's disease.
The couple have decided to go public with Glen’s diagnosis because he's hoping to say farewell with a final slate of live performances this fall – and they want his fans to be aware of the musician's condition.
"Glen is still an awesome guitar player and singer," says Kim. "But if he flubs a lyric or gets confused on stage, I wouldn’t want people to think, 'What's the matter with him? Is he drunk?' "
The Grammy-winner, whose "Rhinestone Cowboy" topped the charts in 1975, had been suffering from short-term memory loss for years, but the Alzheimer's diagnosis only came six months ago.
"I still love making music," says Campbell. "And I still love performing for my fans. I'd like to thank them for sticking with me through thick and thin."
For more on Campbell's story, pick up the new issue of PEOPLE, on newsstands Friday