AITA for not letting my sister use my prom dress?

So, I wear the same size as my sister and she’s going to her prom this year but I went to my prom back in 2019.<br><br>My sister saw my prom dress last year when I showed it to her and she told me it was really pretty. Now that her prom is coming up she started asking me about it and asked if she could use it for her prom too.<br><br>I told her no and she got upset. She said I was being selfish and I don’t plan on wearing it again so I should let her use it but I said no.<br><br>My sister then asked my parents for help but they said it was my choice if I wanted to let her use it.<br><br>She then went behind my back and asked my boyfriend for help. He’s my ex-boyfriend now.<br><br>My ex said that he believed it was my choice but he also said that he understood where my sister was coming from and she tried to use that to make it seem like he was on her side.<br><br>He then offered to take her dress shopping and said he’d pay for the dress of her choice.<br><br>She ended up getting the dress she wanted but acted like a baby about me not letting her use it and got upset that my parents didn’t make me let her use it.<br><br>My parents told her how childish it was to throw a fit and attack me but she just said I was the one being childish and that’s why they wouldn’t help her.<br><br>I feel like I don’t owe my sister anything and I don’t see why I should let her use it but my friends are saying I should have just let her use it and they said there’s no point in keeping it.<br><br>AITA?<br><br>Edit: I would also like to add that my sister is 20 and in college while I’m 23 and live away from my family so I don’t have the dress anymore since I live somewhere else.<br><br>My sister would have had to fly to where I live just to use it which would be expensive and my ex offered to buy her a dress instead of paying for her to travel here to use it.<br><br>Also, my sister and I aren’t close but I would never try to stop her from going to prom.<br><br>I also didn’t say she couldn’t go to prom unless she wore my dress.<br><br>She could go to prom but just not in my dress.