I am so sorry you have lost Max. I, too, had the experience of seeing my little beagle, Quinn, playing happily one day and still in my arms just days later from an aggressive cancer. The kindest thing you can do is shield your boy from needless suffering. It’s quite likely a second opinion would have yielded similar results, but it is perfectly normal to second guess your decision. It had to be extremely difficult seeing Max wanting to go home and knowing if he did, he would suffer greatly. Your final act of love was the kindest thing you could have done. Try to focus hard on happier times in these beautiful spring days and know you gave Max the best life he could have had.
Here is my boy, Quinn, enjoying that same lush grass. I know you love Max just as much as I love my boy. They are frolicking together at the Bridge.