I’m 17 and still in high school. I go to a Christian school and I’m pretty committed to my faith, though I’ve never tried to push my beliefs onto anyone, especially not my family. I’m honestly the odd one out when it comes to values in my house. My sister, who’s a year younger than me, is kind of the opposite. She jokes about my beliefs and sometimes calls me “the priest” of the family. I’ve always brushed it off and tried not to judge her. I love her, despite the differences.

But yesterday something happened that I just couldn’t stay silent about.

My sister has been dating this guy for a few months now—he also happens to be my best friend. We’ve been close since middle school. He really liked her, and I know for a fact he was serious about the relationship. Well, I found out she cheated on him with another guy from our class. I was beyond shocked. I confronted her, and she didn’t even seem remorseful. She just said it “wasn’t that deep.”

That’s when I snapped. I yelled at her and called her a slut. I know that was harsh, but I was furious. She broke my best friend’s heart and didn’t even care. She ran to our parents, crying about how I was being “mean” and “controlling.” They ended up scolding me for being rude to her and told me I needed to apologize.

Now I’m the one being treated like the villain. My parents are big on “family unity” and usually try to excuse both me and my sister when we mess up, but I just couldn’t sit back this time. She hurt someone I care about deeply and acted like it was nothing.

So now I feel stuck. I know what I said was cruel, but what she did was awful too. I don’t know if I should have kept my mouth shut or if I was right to finally say something.

AITAH?