Oh my - I'm so very sorry to hear about this
Do the vets think that this was brought on by an injury? Or more of a genetic defect?
Growing up, we had a dog that had a spine injury due to a fall. The symptoms our dog experienced don't sound very similar to what you're little guy is dealing with, but... Over the course of about a week our dog slowly lost control of her back two legs. I don't know that I've ever cried more in my life than I did during that week, culminating with us eventually having to put her down. The vet treated her with steriods, hoping to alleviate the swelling and allow her spine to heal. It just didn't happen
The only alternative was an extremely expensive surgery that was by no means guaranteed be successful, let alone bring her back to 100%.
In the end, finances played a large role in our decision to let her go, but also the uncertainty surrounding spinal cord surgery...it's just such an iffy proposition. Obviously, that doesn't make the decision of whether or not to say goodbye to a little guy that has become a member of your family any easier.
I'm so sorry