My bestfriend is stealng my used underwear what shouid i do?

she knows im bi-curious bc she's seen some web sites i've been going on and ask me about it. she thinks its a big deal we even went to bi-les-gay clubs before with other friends and hung out with alot of cool people.she knows i wouid never do anything with any of my friends-they r all attractive but it wouid just be too awkward for me. i think i want someone new that i dont know yet. but lately for the past two months im missing at least 8 pairs of thongs and its always when she's around. usually after my shower i put my clothes in the hamper,in the bathroom to be washed and i've noticed when she's here she always goes in the bathroom like right after i come out. then whenever i get ready to wash my clothes im like" where are all my underwear"? i havent said anything about it,but i know its her.now i avoid her coming over or i hide my all underwear.its kind of weierd and i dont know what to do.