Could be just a coincindence meaning nothing.
Or it could be simple folk magic to keep your brother's mind and, um...attention faithfully on this girlfriend. Does his girlfriend use magic? Is it a part of her culture/household?
What you can do: Put on gloves, unwrap the photo, throw away the underwear at one crossroads and the photo at a different crossroads, say a prayer each time for your brother's happiness, walk back home without looking back, don't talk to anyone, and take a shower or a cleansing bath immediately upon your arrival home. Done, no more spell.