So, you have this friend. She's got a boyfriend or maybe is just dating a guy, but she stays at his place on the regular. She's probably got a toothbrush over there. She only sleeps in her own bed (alone or with him) a couple of times a week, but she still pays the electric and mops the floors at her barely-inhabited apartment. Your friend (or, let's be honest, you) is in a "stayover" relationship.
The stayover relationship, a newly-discovered species, refers to a type of relationship among young people ages 18 to 29 in which a couple sleeps together an average of three to four nights a week without actually moving in together. It implies a level of interest and companionship without the commitment of cohabitation or marriage. And it's the new way of life for 20-something couples, according to a study by Tyler B. Jamison, a researcher in the Department of Human Development and Family Studies at the University of Missouri.
While the study only surveyed 22 college students and graduates to determine the pattern (and notes that it did not study the overall incidence), I've seen these types of relationships first-hand in my little 20-something world. Couples simulate living together without taking on all of its responsibilities, like cleaning the other's apartment, combining financial assets or totally merging personal space. You're still a guest of sorts in this person's house, Jamison says -- especially if he/she has roommates, I say. People in stayover relationships also typically do not have keys to their partners' pads.