AITA for kicking my sister out of my house after she tried to sabotage my relationship?

I (32F) have a younger sister, Charlotte (27F), who is my only sibling. We’ve had a complicated relationship ever since we were kids, but we always managed to stay close. She’s funny, charming, and can be the life of the party, but she also has a tendency to get competitive. Over the years, I’ve let a lot of things slide, from small jabs at my career to snarky comments about my life choices. But when it comes to my relationships, I draw the line.

I’ve been with my boyfriend Ethan (35M) for about 3 years now, and we have a great relationship. We’ve been through a lot together, from dealing with personal losses to celebrating successes, and I genuinely thought we were on the path to a happy future. Ethan is the type of person who shows up when you need him, and I love him more than I can express. We’ve talked about getting married and starting a family. Things were perfect, or so I thought.

A few months ago, I invited Charlotte to stay with me for a week while she was in town for work. I didn’t think anything of it—she’s my sister, after all. We’ve lived together before, and I didn’t expect any issues. But something felt different this time. Charlotte and Ethan have always gotten along well, but recently, I started noticing small changes in their interactions.

At first, it was just innocent things—flirting here and there, lighthearted banter, compliments. I didn’t think much of it; it seemed harmless. But the more I paid attention, the more I realized it was crossing a line. I would catch Charlotte laughing at things Ethan said, touching his arm more than necessary, and giving him lingering looks when she thought I wasn’t watching. It made me uncomfortable, but I tried to brush it off. After all, they’re both adults, and maybe I was overreacting.

But then, the situation escalated. One night, Ethan and I were sitting on the couch, and Charlotte came in after a long day. She asked if she could join us and put her feet up, which, again, I didn’t think much of. She sat so close to Ethan that their legs were touching. As I watched them interact, I could feel the tension building. Ethan, who is normally so reserved and attentive to me, was laughing and chatting with Charlotte like they were the only two people in the room.

That was when I snapped. I asked Ethan to give me some space and told Charlotte to go to her room. I couldn’t ignore the way things were between them anymore. I couldn’t tell if it was all in my head or if I was seeing something that wasn’t there, but the vibe felt off. That night, I couldn’t sleep. I kept tossing and turning, my mind racing.

The next day, I confronted Charlotte about her behavior. I didn’t want to accuse her outright, but I told her that I had noticed her interactions with Ethan were becoming inappropriate. I told her that she needed to back off, and that if she couldn’t respect our relationship, I’d have to ask her to leave. She became defensive, saying that I was being paranoid and that I had no reason to be upset. But I stood firm, and after a tense conversation, she finally left the room.

Later that evening, I sat down with Ethan and told him what had been bothering me. To my shock, he didn’t deny it. He admitted that he had been feeling a bit confused and had been caught off guard by Charlotte’s advances. He said that while he didn’t intentionally lead her on, he had been flattered by the attention and wasn’t sure how to handle it. I was hurt, but at least he was honest with me.

The next morning, I told Charlotte she had to leave. I couldn’t tolerate the way she had crossed boundaries in my relationship. She was furious. She accused me of overreacting and told me I was ruining her chance to have a good relationship with Ethan. She claimed that she was just being friendly, but I didn’t buy it. She was angry, and we ended up having a huge argument. She called me jealous, insecure, and selfish for taking Ethan’s side over her.

I felt terrible, but I knew I was doing the right thing. I’ve always believed that relationships should be built on trust and respect, and Charlotte’s actions showed me that she didn’t respect either of those things. Since then, she hasn’t spoken to me much, and I’m left wondering if I did the right thing.

Ethan and I have had many conversations since, and he’s reassured me that he only has eyes for me, but I can’t help but feel betrayed by both of them. Our relationship has been strained since that night, and I’m still processing everything that happened. My parents are divided. Some think I did the right thing by standing up for my relationship, while others think I should have let it go and not made a big deal out of it.

So, AITA for kicking my sister out of my house after I found out she was flirting with my fiancé?