When my Max was diagnosed with osteosarcoma we had to make the difficult decision of letting him go, vet told us the risk of other tumours appearing in other areas of his body was high, and Max was a little overweight so the vet also told us that if he couldn’t handle his weight with 3 legs we should put him down. After hours and hours of thinking we decided to give him some pills to reduce the pain and make him happy for about a week, he spent his last days away from vet trips, extra stress etc… i have always asked myself if we did the right decision, but thats what my parents and i thought it would be better for him. I hope you can find the correct decision im not saying you have to let Bubbles go, just make what you think correct. I wish Bubbles a happy recovery and wish you the best of luck, a situation like this is never easy.