When I found this prompt, Candy Alliance popped up in my mind right away.

Imagine person A of your OTP going out with their best friend, only to get third wheeled because their friend decided to bring their partner along. Person A, who is secretly frustrated but doesn’t want to cause an argument, slowly walks behind the two lovebirds as they bump into person B, who had the exact same situation happen to them. Person A and B ditch their friends without them knowing about it and decide to have a fun time together.