Wow, I am sorry to hear this
@lovedogs. Being a dog lover myself I understand this is a kick in the gut to you.
While words can never sooth the void you are feeling I do hope they give you strength, hope and courage to get through this difficult struggle.
First, stop beating yourself up about the situation. Your baby is unlucky and the surgery is expensive, risky and does not provide a promise of a true recovery. This is the toughest part because we always want to do whatever we can to save those we love. But sometimes we have to embrace the situation and accept it for what it is.
Second, try to enjoy your time. If you read I'm sure you've encountered long and short books. If you found good books, they always leave you thirsting for more regardless of the length. It's been my experience it's far less about the duration and more about the journey. In a sense, you've been given a gift. You understand the "book" is shorter than you desire so maximize every day you get completing it. There will be time to mourn later. But for now, maximize both you and your fur baby's happiness.
Lastly, when the dreadful time comes allow you the time and space to properly mourn. Several years back I had to put down a Sharpei I had since I was a kid. That dog had been through lots with me and had been there when I had no one else. I cried like a 5 year old boy as the vet administered drugs the last minutes of his life, but I had the peace of knowing we maximized our time, while some surgery options were available they were patches and not a fix but mostly in his eyes he was tired and I knew he was ready. To be honest, that hurt for a good year or so. Then a girl I was dating was insistent on getting a pup as we were living together. I was hesitant. Through an ad I then found my choc lab, Stella. She stole my heart and her personality, attitude and mannerisms remind me a lot of my Sharpei. She's not a replacement by any means but rather the current chapter in my life. I cherish her and the time we get for what it is because I know regardless how long I get I am going to want more. My point is keep faith. This is a portion of your journey but your baby is preparing you for the next segment and you don't even know it.
Head up. And smile. Hope you have a great day!
