My las experience with a dog, is similar in some respects, but very different in others. I'll share it if it might help.
Briefly. The animal was owned by a rather unplesant man I knew, but associated with for other reasons. He continually beat the little thing, not because it had done anything wrong, but simply because it was the only thing he could hurt and get away with it. The dog, when I met him was so nervous, it vibrated, continuously.
I managed to take the dog, when in a fit of temper, this guy said he was sick of the sight of it.
I lived in a single room in somone's house. I couldn't even have visitors, let alone a dog. But I managed to get someone to take it for a few nights, while I found somewhere else. Over the next couple of years, this became a bit of a habit. I would find people who would take him for periods, ranging from a few weeks to a few months, but always, I had to find somewhere else. I should say that all of the people he lived with were kind and decent people. Sadly, this wasn't the prettiest dog in the world. He was certainly no trophy, especially for the fashion conscious.
I visited the dog regularly. I trained him to follow commands. He quickly became devoted to me. He seemed to try to work out what I wanted and would follow almost any command. He would walk along a raod, no matter how busy, at my heals, without a lead, for example and stop when I said. But more than anything, and this is where he was so similar to your dog, he was utterly devoted to me. He would look so sad whenever I went away.
Anyway, I had to go to Europe for a while. While away, he was staying with some people who had had a baby. Apparently the dog let out a short growel when the baby was being attended to.
When I returned, the dog was gon. I completely understood. The baby comes first of course. But they wouldn't tell me where it had gone. They claimed he was on a farm, but wouldn't say where. (Usually, you tell kids that their favourite pet has gone to a farm).
I suspect, they took him to the countryside and left him there. If I could have done, I would have taken him to a vet myself and had him put down.
I will say this. I would rather have sat with him, holding him while he died, than to know that he probably died alone and frightened in some country wood, with a 12 bore bullet in his rump.
I'm really sorry to have to say this, but take him to a vet and sit with him while he dies.