Me (28f) and my sister (32f) always had a rocky relationship. Growing up with her was difficult and I don't actively have contact to her outside of family events.

She met Alex when they both were 20 and they dated for ten years, but eventually broke up due to reasons she didn't want to tell us. Shortly after, she started dating Marc (mid 20s) but didn't want to introduce him to the family for about a year or so (we all live like ten minutes away from each other, distance wasn't the problem).

It became interesting when our parents kept on meeting Alex' parents, because they became friends during those ten years. They found out that Alex broke up with my sister because he had found out she was dating another guy (Marc) behind his back. And she just kept on dating Marc after Alex broke up with her. She didn't know we knew this and I'm guessing she didn't want to introduce Marc to us because we'd figure out. She did, however, bring him to one of our family events eventually because our parents were asking constantly.

The thing is, the more I got to know Marc, the more I realized he didn't know anything about the whole Alex story, like at all. He simply believed that Alex was her "gay best friend" and they had a falling out at some point. So here's where I might be the asshole: I purposely asked questions about their relationship, like when they started dating, how they met etc. and Marc eventually caught on. He sent me a message that evening (I never gave him my number but he got it from my sister's phone) and asked what I meant. I proposed meeting him to fill in the gaps. So yes, I actively sabotaged my sister's relationship, but I felt so bad for this poor guy and I couldn't be the one enabling my sister's behaviour. She's obviously not talking to me right now, which I honestly don't mind, but we have a family vacation lined up and my parents want me to apologize to keep the peace. AITAH for being so upfront with him, should I just have minded my own business? Any advice how to go from here is greatly appreciated.