You and your girlfriend had a conversation about hall passes, you know; that one person you'd let your partner fuck in a committed (monogamous) relationship. You obviously chose your favorite celebrity, because you couldn't imagine having to pass up the chance to fuck her if it presented itself. Your girlfriend on the other hand chose someone way more attainable... Your best friend. Honestly if it was a one time thing she would be more than happy... sooner than later too, because she's really been craving some new dick. Actually, could you just send him some of her nudes and let him know he has your okay to fuck your girlfriend? It makes way more sense coming from you... Hopefully this stays a one time thing, could you imagine if your best friend fucks your girlfriend more than you get to?