I don't necessarily believe in a rainbow bridge for animals... but I think what I believe may be of more comfort than that.
I think that when you've lost a dog that you love very much, then he will stay close to you, and you will find him again. May not be right away, and you might not recognize him immediately, but you will see bits and pieces of him in dogs you love and cherish afterwards.
Back in December of 2007, we lost our almost 14 year old little golden to cancer of the spleen. That dog had more character and clownish attitude in him than most dogs. There were little things he'd do like KNOWING where all his tennis balls were and coming to find you to get them out of a difficult place for him, and then trotting into our livingroom TRIUMPHANTLY with that ball in his mouth to physically THROW himself down on his back and balance the balls between his front paws while he mouthed them or whatnot.
And Sammy was also one of those leaners, who would come up and lean on you or sit on your feet or use his nose to nudge your arm up so you would pet him....
And he was one of those creatures of comfort dogs whose favorite sleeping spot was curled up on the same pillow as one of his people.
There are various other things he would do like the full out prancings and strutting, the sideways looks, the random winduphisbutt zoomies, the I'm-crazy-and-love-the-world attitude...
Jacks grew up with our docile-sweet-gentleman-unassuming-faithful Danny and there are many times where I see him sleeping or sitting quietly looking out windows or over the distance that I see my Danny in him, but there is a lot of Sammy in him as well, even though Jacks was born 3 weeks after Sammy passed.
After Sammy passed, my oldest sister (he was her heartdog) was heartbroken. We adopted a collie shortly before bringing Jacks home, because I felt that it was very important that she have a dog to bond with and love to help her heal. And he did. Arthur is one of those special collies who "recognized" her when she went to the foster home to see him the first time. The foster lets the dogs choose their owners, because a lot of them are naturally reserved and suspicious of people. Sometimes if a match isn't a match, the foster can see it right away. With Arthur, he immediately went up and jumped up on my sister, touching her face with his long pointy nose. I think my sister's heart started to heal right from that point.
At the same time and in the years since then, I can't tell you how many times she's stopped and looked at me when Jacks has done a "Sammy thing" like sitting on her foot and giving her the sideway look. Or rolled his head back smiling.
Sammy - for what its worth, already had a lot of traits from his brother (our first golden) who helped raise him. When Charmy passed away, within a few months Sammy's strawberry blond coat really started turning red. It probably would have happened anyway (he always had a pinkish color), but it was really weird how quickly he darkened after Charmy passed. We joked that it was the one way that Charmy chose to remind us that he was still with us or something.
Comfort will come if you open up to it. Don't bury your heart.