My cat refuses to stay at our old house after we moved back

Last January, we moved to a new house, and my male cat adjusted really well. He stopped roaming around as much as he used to at our old place. He became really fat and mostly stayed at home, aside from going out for a few hours sometimes.

There was also a cat living next door at our new house. That cat arrived around the same time we moved there, and they used to hang out together every day (although they never really played with each other—they mostly just stayed around each other).

Now, we recently moved back to our old house. On the first day we got here last week, my cat was extremely vocal and kept insisting on going outside. Up until now, he still doesn't really come home except at night, and even then, he doesn't sleep here. He's also very loud whenever he's here.

What's worrying us the most is that he hasn't eaten here even once. He does drink water, but he doesn't eat any of his food. Every day, he comes home smelling strongly like fish, so we're wondering if someone else might be feeding him.

For context, there are a lot of houses behind our compound, and he used to roam around that area even before we moved to the new house.

We're really worried about him. 😢 Is this normal behavior for a cat who has been moved back to a place he used to live in? Could he be looking for the cat he became attached to at our previous house?

Please help us understand what might be happening and how we can help him adjust. We're really worried because he barely stays or eats at home anymore.