Cohabitation.

Co·hab·i·ta·tion
n.

[L. cohabitatio.]

1. The act or state of dwelling together, or in the same place with another. Feltham.

2. (Law) The living together of a man and woman in supposed sexual relationship.

It's weird to think that since 2001, I have had 18 room/housemates in 7 different houses in three different cities.