By Seamus Duff Boyzone fans have been left stunned by the sudden collapse of singer Keith Duffy’s marriage – after he was married to his wife for decades. The 49-year-old Irish singer has been living in the spotlight since 1994 when the boyband he is a member of burst onto the pop scene with debut single Working My Way Back To You. Keith shared the spotlight with Mikey Graham, 51, Shane Lynch, 47, Ronan Keating, 46, and the late Stephen Gately \- who tragically died in 2009 at the age of 33 due to health complications caused by an undiagnosed heart condition. But there was someone else at Keit…