QRTRHRS, I'm not familiar with the term 'Rainbow Bridge, but I am, sadly, most familiar with your sadness. My first dog was a German Boxer... loved that rascal for 8 years. We were best friends, until a renting neighbor stole him. I loved for Duke for weeks on end but never found him nor the sorry azz neighbors.
I share your sadness comparing to my own these last 3 months. We lost one of our two Toy Rat Terriers back in December. Little Bleu was with us for 15 years. He was never totally healthy, but he was always lovable.
Then in February we lost our only ever cat Cooper. The local feed store named Cooper's Feed Store, had the little kitten in a box near the door, for free. At first sight my SO 'had' to have him, and so named him Cooper and brought him home. At first Coop, as we usually called him, was terrified of our two little 5 pound Toy Rat Terriers. Yeah - they gave Coop ****. That is for about a year... until Coop began developing. Coop proved to be a Maine Coon breed, and at the untimely death Coop weighed in at 22 pounds. By then Coop would just strut around like he owned the place, and of course, he did.
Coop took to the SO pretty much as his 'mommy', generally shying away from me until about his last year. In his last year he'd occasionally sidle up to me as if in some sort of treaty or guarded companionship. We'd begun taking occasional walks around the lake together, with me giving him plenty of time to explore. Coop loved going into the woods during the day and usually bringing back a 'trophy' into the house to show off. Sometimes Coop would simply walk up to a large tree and jump up 8 or 10 feet up, just to exhibit his strength. Unfortunately, last month he apparently fell wrong, breaking his back, rendering him totally helpless.
In the end, most sadly we had to allow the Vet to put down both Bleu and Coop. Both were very loved and lived a wonderful comfortable life while they were with us. I built caskets for both and buried them in their favorite spot here on the place. I make a point to say hello to them as I pass by them on my daily walks. They will never be forgotten.
Reminiscing about our recent losses perhaps doesn't make it any easier for you in your loss. But you can be sure, I and others have gone through the same sadness and share those feelings with you in the loss of your friend Desi.