I kinda get what you mean but thinking about it, I really didn't try to think of jonggu as just a dog before... and now he has an personality, thinking and feelings and he wants to make his master happy and left him because he didn't achieve this even after he turned into a human and he is sad because his thinks his master see him as a dog not a human... Look it's complicated...I think it doesn't sound like the thinking of a dog anymore..in the end this won't happen in reality so I guess I will keep thinking of jonggu as just the way he is now it's not like he can be a dog anymore either
"Sorry I really wrote a lot lol"
Well tbf, Jonggu is in love with his master. He wants him to be happy, but he can’t stand watching his master be happy with someone else. His master continued to disregard his emotions and feelings and even began dating red hair dude despite knowing Jonggu had feelings for him. They even had sex with Jonggu around. Jonggu is going through so much pain and is tired of pretending to be happy for the sake of his master, so his actions make sense. He isn’t a dog anymore, but his master still sees him as a dog. So bam, master forgets him and stays with red head, and Jonggu can hopefully live a normal human life without him and move on. Ofc, that’s not how it’s gonna go.

JONGGU FUCK OFF DON'T DO THAT TO HIM AND US SERIOUSLY MAN DON'T
He is dying for finding you what are you trying to do
Someone tell that dog God or whatever he was to tell them to get their shit together