Yeah, for a brief overview of the setting, there are seven realms. You live on Terran (Earth), and each new episode takes you to a new realm for a self-contained story that serves to move the overall story and characters forward.
There are three main love interests. One who you are with by default, and two who are optional (but are still main characters regardless of whether you are in a romantic relationship with them or not).
The other ladies in the game will reappear at various points throughout the game and will have their own "side paths" where you can get to know them better. However, you are not "in a relationship" with them. You can see those outside of the main three as more of a friends-with-benefits situation.