(For context, all our ages are slightly aged up but close to our real ones)
Yesterday I(16F) told my neighbors, M and C(both 12F), that I had a crush on their step brother L(15M). Who is fifteen. I told them because I trusted them enough not to tell him. Plus everyone thinks we'd look cute together and we have relatively similar personalities. I am pretty sure that L likes me back at least a little bit.
Anyways, my sister, MD(13F), was also in the room when I said it. And then today. I was hanging out with MD, and she randomly told me that she also likes L.
I was very upset by this. As I liked him first. And he is too old for MD. She also never seemed to like him until after I told them that I liked him. I'm not sure that she genuinely likes him and I think she's just trying to fuck with me by saying this. Because she knows that I like him a lot and want to be with him.She also proceeded to tell me that she was going to try and get with him. I tried to nicely ask her to not try that and to just let me have him. But she refuses to back off about and just leave it alone.
After we had that conversation, we were all hanging out in my basement. We were playing a board game and MD decided to sit next to L while there was plenty of other seats open. She also kept side eyeing me whenever I would interact with L. As well as when C or M made comments about how me and L would look cute together. She would give me the dirtiest looks for no reason.
MD also has a girlfriend already. And when i confronted her about her "crush" on L and what she would do about her girlfriend. She just said "I'll just break up with her" as if it was the most casual thing to say. Which I personally think is not okay.
I don't think that she should've told me that she likes L when I liked him first. She could've kept it to herself and didn't need to share it. But I also believe she may be acting like this out of spite. Even though I don't think l've done anything deserving of getting spited by her. Or I have and I just don't realize it. Anyways, I could use some opinions on this. I’m not sure if she needs to back off, or if im just overthinking it.
If she does need to back off, how can I try to get her to?
TL;DR/ sister wants to try and ruin my potential relationship with my crush. Only after I told her that I like him.