I Caught My Brother Wearing My Clothes

A couple nights ago, I came home from volleyball (I'm a senior) and my parents were at dinner for some thing for my dad's work. I knew my brother was home but I thought he was doing his homework or something so I ate downstairs and didn't announce myself when I got home.
Long story short, I walked upstairs and saw my brother (sophmore) dressed head-to-toe in my skirt, my top, and wearing makeup. He stared at me for a little bit while I sat there staring. I started laughing and found it hilarious (and kinda flattering?) but I obviously had a lot more to think about.
So I forced him to talk about it and yeah.. He full on wore my clothes for a long time. He wore my panties, and that is super gross so I told him this had to stop... Well at least some of it. I told him the following things: His makeup wasn't awful but if he wanted to do makeup, he could just ask me. He shouldn't wear my clean clothes and then put them back in my closet, cause I wouldn't want to wear them anymore. And that he needed to stop wearing my underwear completely.
After talking until my parents came home, I decided not to tell them and my brother begged me to keep it a secret.
So here's what I'm thinking... I really want to treat him and take him to the mall one day, but I don't know where he would "hide" this stuff or if he would be too embarrassed. He's shy about it but I can tell he enjoys it, he's not gay but kinda acts like a girl. So yeah that's my rant about my brother.