she's a scorpio isn't she? mwahaha. wow, sounds like my situation with my ex, only, she doesn't bring her new boy toy here, she goes to see him. There may be reasons for living with exes. Leases, or just financial situations leave the trapped, you'd have to pretty much remove her from the situation somehow if you wanted to convince her to do that.
be it moving in with your, or convincing her to "help out" a friend of yours with his/her rent by being thier roommate.