Feminine Reader

You often steal his aviator jacket--he doesn't mind, saying it looks cute on you.
OR
You often steal his aviator jacket, and you two wrestle for it.

He often takes your kitty hoodie, or any hoodie on general.

Masculine Reader

You often steal his t-shirts, seeming they fit you just right. You've kept a couple.

He often steals yours too, but only any dark-shaded ones because he's embarrassed of anyone knowing it's yours (he often wears something overtop so no one sees it).

Feminine + Masculine Reader:

You sometimes steal his shirts, seeing they fit you cozily, and you kept an old sweater of his that you wear when you're in a cuddling mood.

He sometimes steals a pair of your jeans if he needs to do the laundy. (Don't worry, they fit him perfectly and you think he looks perfect in them.)