It’s very considerate of you to suggest three months sexually off-leash, as she is traveling to the ancestral homeland of male supermodels, where a chunk of the GNP is dependent on Carnival -- a weeklong drinking, samba and sex fest.
The problem is jealousy, one of our guard dog emotions. Evolutionary psychologist David Buss explains that jealousy rises up automatically to help us fend off “potential mate poachers” and prevent a mate from “defecting.” Because it’s set on “auto,” it can be hard to override.
That said, though you don’t have a committed relationship with this woman -- let alone an open one -- you might be able to make use of a psychological tactic of people in sexually open relationships. It’s called “comparison” -- taking pleasure in your partner’s getting pleasure, even if it’s from some other, uh, provider. Granted, this is probably about as realistic for most people as their Ubering to a party via unicorn. However, it dovetails nicely with my fave quote about love, from sci-fi writer Robert Heinlein: “Love is that condition in which the happiness of another person is essential to your own.”
Float the idea of planned cooperative ignorance, and ask her to think on it for a few days. People often have more reasoned responses to hot-button issues when they aren’t expected to reply pronto. Also, it doesn’t hurt that she’s the one wintering where stone-sober women are tempted to stop men on the street with “Excuse me, but would you mind if I licked black beans off your ridiculously chiseled abs?”