Its amazing and such a wonderful thing how pets become such a large part of our lives and really do become part of the "family" dynamic. Never forget the great times and know that you are doing the right thing in not prolonging his suffering. It's such a tough decision but it's selfless on you and his moms part. I wish I knew what more to say but I don't feel like crying at work. It's going to be a rough few weeks, stay strong and allow yourself to grieve