Be aware of the double standard.
Maybe it's human nature or because karma revels in irony, but sometimes, despite your best intention to remain stoic and emotionally unavailable, you will feel feelings. Some semblance of concern will creep in. She'll admit she's seeing someone else, and your face with flush with anger.
What, you thought you were the only one who enjoyed the freedom? False. Independent, free-spirited women have been around well before Beyoncé was singing about them. Still, they may surprise you. You might be tempted to tell her she's not allowed to see other people, despite the fact that you also are. Try again, buddy.
She's free to let her freak flag fly, just as you are. If you'd like her to stop seeing other people, you might want to call it quits with your trio of lovers, and tell her your feelings have changed.