TIFU by not saying happy Birthday to my Brother in Law (on purpose)

My Brother in laws birthday was over the weekend, he and my sister went abroad and before going I messaged my sister “have a wonderful time away for (BIL) birthday!”.

When it came to his birthday, I admit I was being petty, I never wished him a happy birthday mostly because he never wished me a happy birthday. Not only that, I overheard him call my partner and father of my child a “dickhead” and “useless fucking idiot”. So I can’t help but be petty. I’ll stand by my partner before I stand by BIL.

I fucked up by not telling him happy birthday, and now my sister is upset with me. She is unaware that I overheard her husband say those things about my partner, and I haven’t brought up that he never wished me a happy birthday. It’s tit for tat, I know I’m an asshole and I know I fucked up 😬

TL;DR: didn’t wish BIL happy birthday through pettiness, have upset my sister