I know exactly where you are coming from also Hush. Had to have my devoted Yorkshire terrier put down just before christmas aand he was only 5. Developed a stomach ulcer from being tormented as a pup by a builder on a site we lived in where work was being done(large complex). This was happening unbeknown to us.
Unfortunately it was not picked up quickly enough and complications caused him severe discomfort to the point he would be walking around, and stop mid stride with severe craps. Poor little guy. Eyes have just welled up typing this.
Hardest decision I have had to make in a very long time, as to look at him, there was no visible signs of any problem.
Vet did a great job, very caring, but yes I cried like a baby as well.
Feel for you man.
heers Brett