Is this game a harem? Or just had sex with a girl, and then went about his business?
I'd say it's more of a relationship builder than can go in a harem direction.
Some characters are up for casual sex as you build a relationship that then gets serious, while others won't want to do it until after you're in a relationship. In the future, some small groups will get along and won't mind/can be convinced to share, others won't be as fond.