This visual novel shows promiscuous activity, i.e. characters engaging in sexual activities with several partners without getting into a relationship with them.
It is also possible for the characters to be in a relationship while having sexual encounters with other characters, yet that does not change the relationships in a meaningful way.
Note: Please do not confuse this with Group Sex, engaging sexual encounters with multiple partners does NOT have to happen in the same scene.
Unavoidable Sexual Encounters with Multiple Partners