For a while the idea of a mechanic has been going around in my head, if the girls are willing to have a polyamorous relationship with each other, it would be interesting that the girls who are not in a couple with Null can become girlfriends with each other. For example, girl A and girl B are best friends, but they are not in a relationship with Null, Null goes out with girl C, girl A asks Null if he thinks girl B would be a good partner, so the player has control with his opinion that they form couples that they like or not, and when girl A and B are a couple, if you have enought trust and love with both girls, they can ask Null to join their relationship, making it easier to go from a monogamy run to a polyamorous run. Even if you don't want to left a monogamy run, can be nice to see the others girls having a relationship.