I'm so sorry, Rosie. I constantly complain about my one cat, and often say I'd happily give her away to a good home. Last week she had to have surgery and I've been playing nursemaid and am totally blindsided by how concerned I've been about her. They really do get into our hearts.
It sounds like you gave him a happy life. It hurts to say goodbye, but you are doing the right thing. Hugs to you and the kiddos.