The mutual attraction between two friends that is acted on in a purely sexual manner. The individuals do not consider themselves to be bound by the constraints of a "relationship." They are merely friends in all aspects except for the added bedroom "benefits."
Alternately, a committed pair who officially "break up," though continue their sexual relationship.
b] Although Joe and Mary broke up two months ago, they still have a lot of sleepovers. Must be a friends with bens situation.