Replying to Who is in the wrong

I let my buddy borrow a helmet for a ski trip and he won’t give it back. This is my backcountry/all mtn helmet it’s a smith vantage. He says bc I have a helmet I use as a beater (giro ledge) he should keep the helmet bc he doesn’t have a ski helmet and can most definitely afford one. We both go to what I would say a pretty prestigious private school. We got it from the lost and found it had been there for a number of years so I told him to grab it bc I had already been in there. He thinks he should keep the helmet bc he stole it but he didn’t know what a smith vantage was until I told him. He has a triple 8 skate snow which he’s convinced is just a skate helmet. I just want your opinions.