My (22f) sister (19f) is making future plans with my ex-fiancé (25m) days after he cheated and I called off our wedding. Am I right to be upset?

I was supposed to get married on the 31st of December 2023, but less than 2 weeks before that, I discovered that my fiancé was cheating on me. I immediately called off the wedding and ran to my parents’ house. It was a very stressful time and a lot happened in a very short space of time.<br><br>My sister is currently at university, but she came home to attend my wedding. When it got called off, she said she’d stay with me at my parents’ house for a bit. I appreciated her support, it felt like she was the only person who didn’t take the whole thing very seriously and could be a good distraction from all the craziness.<br><br>However, when I found out that she was in touch with my ex, everything changed. She never mentioned it to me, but I saw a text conversation on her laptop one day. My ex was making future plans with her, talking about meeting up in January when she’d be back at university.<br><br>I was absolutely devastated. She is my baby sister; I would do anything for her. Finding out that she was making future plans with my cheating ex felt like a betrayal and almost as hurtful as his initial betrayal. <br><br>When I confront her, she became defensive and said that she was sorry and didn’t know how to act in this situation. I screamed at her to stay away from him, and she agreed, saying she hadn’t planned on meeting up with him anyway. I asked her why she was even making plans with him then, and why she didn’t tell me about it. <br><br>Now we’re not speaking. I’m still staying at my parents house, and it’s very awkward. She keeps saying that she didn’t do anything wrong and it was “just a conversation”. I don’t know what to do. I’m in need of advice.<br><br>Am I overreacting and should apologise to her? I don’t know how to feel right now.