I gift my girlfriend with anal sex on Christmas, but I'm taken aback by inviting her friend

I've been waiting for this day for a while. Not because of the presents, but because my girlfriend has been hinting at something special. She knows I love her ass and she's finally ready to give it to me. I've been dreaming about this moment, and now it's here. I walk into the living room and see her standing there, dressed in a sexy outfit that leaves nothing to the imagination. She's been a good girl all year, and she's ready to show me how much she loves me. But there's a surprise - her friend is there too. She's eager to join in and watch as I give my girlfriend the best gift of all - my big cock. I can't wait to see what happens next.