Pretty sure it was a British movie and it was about these boys at private school. One of them kills the others girlfriend and dissects her leaving her for the school to find and the ending has the main character accepts his fate and takes the dead girls head and leaves the school ( she was his Mary magdalene) does this sound familiar to anyone?
Can you give us more info? What decade was this made? Was it black comedy or straight horror?
Only ideas that are remotely similar, that come to mind, are PATHOLOGY and TORMENTED.