What you (I) can (should) wear from your boyfriend's (brother's) closet:
First of all, if he is letting you wear his Givenchy shirt, he is a keeper.
One man's home-wear is another wo(man)s coat. (Derek Rose)
Shirt/Dress/Skirt - "But I style it much better than you do!" (Acne)
This one is to keep his smell on you (ew, if its your brother.) (Maison Martin Margiela)
"Let me carry that for you." (Raf Simons)