Sorry bicurguy321, you are not gonna get much support or sympathy on this one. In the first place, you violated a woman's privacy by trying on her clothes. Not just any woman, but the fiancée of your roommate.... Top it all off, she is your girlfriend's sister!
It's one thing for a young boy trying on his mother or sister's clothes, but wearing someone else's clothes without asking is about as wrong as it can be. You are old enough to buy your own clothes and lingerie...you are an adult! I wonder how you'd like your private things taken and used without permission.
Be lucky if your roommate does not beat the daylights out of you and throw you out or leave over this.
You may, in the end lose a roommate, he is also a friend I assume, a girlfriend, and friendship of his future bride. Not to mention the trust and respect any of them will have in you. I would not want to be you right now.
I don't care how good a friend a guy is, if I found out he was wearing clothes or lingerie of my SO, we would be done as roommates and friends. That is if he was lucky to get away without having his butt kicked!
