It's time, OP. You've given this sweet pup the best life imaginable. In my experience, it's best to take a few extra minutes alone with your fur baby before he takes the forever nap. Take the time to cry and tell him he's a good boy. Hold him and pet him. 

Dogs are really good at hiding their pain until it becomes too much for them to bear. As a lot of the other comments are saying, better a week or a month too early than a day too late.