Am I being selfish?

Most of my friends are spending New Years with their families, so my best friend and I just planned to go to her cousin's house for something small. She then decided to invite a guy she has had a long time crush on, which automatically had me feel like a third wheel despite them not being together. I sort of hinted that I don't have to go if he goes and she didn't say anything, so should I just not go? I just don't feel like spending the holiday alone, but I also don't want it to be an awkward night. Am I reacting selfishly?

I don't think you are being selfish. It's your friend that expects you to chaperone her New Years date that's being inconsiderate. The ideal solution would be for you to have a date also, otherwise I would find something else to do.