Dude isn't doing anything wrong. It is not a bad thing to be nice to others. That's the only way the world gets better is to all get along better. The only problem seems to be a difference in cultures (along with what seems to be some undiagnosed psychosis on the ladies' parts.)
Let's assume the script actually was flipped, with all the primary characters getting genderswapped.
This would be the most horrifying thing to imagine in a society like IRL:
A girl suddenly finds herself alone and afraid in a world not her own, with a society relatively alien to her, yet scarily familiar with a boy:girl ratio of 5:1. After her 'male' caretaker gets her a job at his hostess club, she finds a nice guy (possibly an above average mob-esque guy) who helps her pick her classes. She does not realize her new friend is now obsessed with this new, kind, pretty girl, and frequently makes up delusions about keeping her to himself. The kind girl, while working at the hostess club, ends up being tied down to a single, lonely salaryman during her only shift, who then begins stalking her due to a perceived romantic attachment. It keeps going. Little boy gets flustered when pretty college girl plays basketball with him. Shut-in NEET gets way too into trying to change his image when his pretty tutor that his mom found shows interest in his hobbies. And it's all because of what? She's nice to others? What is she supposed to do, be a bitch?
I don't really think there is a safe way for this story to go. Even though the first chapter foreshadowed the idea of a harem ending, with polygamy being hinted at as a viable option, does anyone here actually believe the leading ladies in this series will really be okay with sharing him? Polygamy works in other stories because it had already been in place before the MC arrives, and the Female Leads already knew it was an option. They can come to terms with it ahead of time, and are already amenable to the arrangement due to cultural norms. Even if polygamy becomes legal by the end of this story, unless the girls actually come together, and are, at the very least, on good terms with each other, this story is only going to end in heartbreak or tragedy.
And at the first hint of that, I'll be dropping this series.