Returning a puppy after 3mo adoption

Heartbroken to be writing this but I need advice.

Me and my gf just moved in. We decided to adopt a puppy and 2months in he developed a limp in his rear leg. He is 9 months old. We got him when he was 6mo. We took him to the vet and racked up a $800 vet bill for x rays on both rear legs. We were told he had hip dysplasia and later got a call saying it was worst and he had necrosis in his rear right leg which is his limping leg and his left is in bad shape. We were informed by the vet that his limping leg would need to be amputated and his life after would change requiring him to go to therapy and also the surgery would be 2-3k and also be on pain meds. Due to financial situations and no one being home 24/7 I contacted the organization in which I adopted him and asked if they’d be able to take him back and explained my financial situation. They said they’d be able to cover the surgery free of charge if money was a concern for the surgery. Am I a horrible person for wanting to return him due to not being in the best financial position and also since he’ll have a big surgery with a long recovery time I don’t have anyone to care for him while at work. I have gotten close to him and it kills me but it’s the best option imo but it saddens me that he was given a bad deck of cards.