Not that I've any personal experience in this practice, mind you, but I hear girlfriends don't exactly take well to being 'loaned out.' In fact, they have their own, special term for it: "Time to dump that asshole."
We guys, of course, love being loaned out. In fact, some of us do it ourselves. Girlfriends have their own, special term for this, too: "Time to dump that cheating asshole."