This seems to be the type of story where the npc are actually real people in another world, which is why it's isekai.
That said, the MC had no way of knowing this when he started. It's really sad but he was looking for love from what he thought it was AI. And I guess he thinks he pas regected by AI as well. I wonder if he already thinks they might be real people now that he and everyone is stuck inside the game.
My guess is he still doesn't think they are truly real and treats them like they are because he hopes to be loved.
I also guess he isn't going back to his original world because in this type of story, people who have nothing to tie them back never go back. Most don't even try to go back.
It's good but... 1- the SA at first was so uncalled 2- i love isekai but while knowing they didn't die irl (yet?) And have intimacy with NPC hold me a bit. Unlike some isekai where the MC die and is totally involved with the new environment or MC interact with other irl players this one is about the MC and a NPC so it feels like he's falling for a bot idk... Correct me if I'm wrong and the Duke was someone that exist irl. I like the story but I feel sad for the Mc bc if he return to the real world after "finishing" the game, won't he end up alone? I want to keep reading but there's something that make it differ from other isekai and a bit destabilizing