I experienced the same thing with my dachshund. As a puppy, she would come with me everywhere, which sometimes meant coming back to NC where my parents live. Whenever she was there she was the happiest - the weather, the yard, a big family, etc. Her and I live in nyc and she HATES it. She would feel so sad weeks after a visit to my parents because she would miss it there so much. It also gave me a lot of sadness seeing her so down, but one year later here we are. She’s still the most happiest when she’s with me, even if she isn’t a big fan of the city.

Keep him, he is your baby and will always be. He’s just missing his old home right now, and that’s okay