One episode in season five of How I Met Your Mother, called Hooked, revolves around people being kept on the hook, romantically speaking, by members of the shows central gang of friends. I cant be with you right now is the phrase the pals keep using to string these people along, the right now leaving the door cracked open just enough that apparently some poor guy is willing to continue to do Robins laundry and rub her feet for the vague possibility of a someday relationship.
This does not make the friends look very good, obviously, but keeping track of and keeping in touch with alternative romantic prospects is a common thing for humans to do, even if it is rarely in such an exaggerated, sitcommy way. A recent study published in Computers in Human Behavior dubs these interactions backburner relationships. A backburner, as defined by the study, is a person to whom one is not presently committed, and with whom one maintains some degree of communication, in order to keep or establish the possibility of future romantic and/or sexual involvement.