Jams,
I have had to have 4 of my dogs put to sleep and it hurt very much, but was the best thing for them as I couldn't bear to watch them suffer. Every time I said I would not get another dog, but I was lost without them and I now have two Poms that I got to replace the last two that I had to have put to sleep within a month or so of each other. There is no easy way to do it. I felt like I really let them down, but they are far better off now. Whatever you decide, it won't be easy, but once it is done and you have a few days to get over it, then it will begin to make more sense.
Ron