So my sister, F19, and I, F15, are pretty close with one another, enough to go out with each other on the weekends and lending each other our things. This past weekend my sister was going out on a date and asked me to help her out and get ready. I happily obliged as I want the best for my sister and she seemed pretty excited. One of the things I did was let her borrow a pair of Converse that I admittedly don't wear too often but are fairly expensive nonetheless. I figured that I shouldn't be too worried because my sister takes care of things that she borrows so I could let her use some of my more expensive things as it was an expensive restaurant they were going to. As she doesn't live with me I told her to just bring the shoes back whenever she could. Well today her and her boyfriend came to return my shoes but when she returned the shoes she told me that the strap tore off of it and showed me. When I looked at it I saw that the strap hadn't been completely torn off but it was unrepairable. I looked at her bc and got mad, asking how it happened as I've had them for a bit and the strap shouldn't just tear like it did, and that it had to have been from neglect. Both her and her boyfriend denied that but didn't say a reason as to how it was almost completely torn off. Still fuming I told her that if she ever wanted to borrow my stuff again she'd have to pay for a new pair of shoes to replace mine. They both got mad saying that I hardly ever wore them and it was an accident and that I shouldn't be so mad about it or ruin our relationship because of it before they left my house. So am I being a butt face?