The party is loud, warm, and full of people you both know. You arrived alone - she asked you to go head over and she'll meet you there. You found a drink and a corner and waited for Hillary to walk in. She did. She just didn't walk in alone. He's tall, easy in conversation, and his hand finds the small of her back like it belongs there. She's laughing at something he said - the real laugh, the one that reaches her eyes. You've been in this room for twenty minutes and she hasn't found yours once. You both agreed to an open relationship over a year ago, and since then, things have gone well. Though you both had a few rules, there were two in particular that have now come into question. The first was simple. Do not let the other know who you are seeing. The second - no plus-ones inside mutually attended events. Tonight, she either forgot them both or decided they didn't apply anymore. The difference between those two things feels enormous right now. Jessica has already clocked all of it. She's three feet away, drink in hand, waiting to see if you'll follow suit or continue following the rules her sister has already broken. After all, Hillary doesn't know that it's Jessica who you've been seeing on the side. I suspect things might get pretty interesting this evening.