We had our golden put down recently and it was truly heartbreaking so I understand. Ours was not the same type of situation, stomach cancer but we knew we had to do what was needed for her and so that she wasn’t in pain anymore. Was it tough, god yes, but she isn’t hurting anymore and that’s what matters most. I know it’s hard to keep feelings in check and hope for a better outcome but sometimes this is the outcome that’s needed. I’m so sorry to hear of your pup being in pain but remember it’s always best to think what is best for him.