My boyfriend pressured me to open our relationship to be "modern," and I finally agreed out of sheer fear that he'd leave me. The result: at the graduation gala last night, he showed up with my best friend, the very same one who swore she'd "help us take the next step." I'm devastated and I don't even know what to say to them.

Short and sweet: this isn't modern polyamory, it's just a dirty trick concocted by two people. An open relationship is based on absolute trust, enthusiastic consent, and clear rules—not on emotional blackmail where you capitulate out of fear of abandonment. Using your own best friend as a guinea pig while she plays the benevolent mediator isn't cutting-edge, it's a massive betrayal served on a silver platter. You have absolutely nothing to justify, nor any "modernity" to prove. Your only role now is to set a non-negotiable boundary. A group message or a curt text will suffice: "You two make a great team of hypocrites, have fun without me." Then you cut off all contact. Losing a selfish boyfriend and a fake friend in a single evening hurts like hell in the moment, but it's the most beneficial cleansing of your entire student life.