Tough one. Personally I feel like a lot of this teenage crap is attention seeking behavior. By you and your son giving him some attention, it could be getting the results he wants in a weird, perverse way. I'd ignore it and try to counsel my son and the girl on why I choose to ignore it. Sick people just want attention and they don't care if it takes weird behavior to get it. I would only take action if he made ignoring it impossible. If he's threatening to harm himself, I can ignore that. Threatening to harm others is a different story.
The kid's not sick, he's heart broke and he's not old enough or experienced enough to know how to deal with it. He wants the girl, she doesn't want him and he doesn't know how all that works yet. Once he realizes there is no hope, and a little time passes, he'll get over it. He's not looking for anyone's attention but hers. He had it for a minute, now he doesn't and he's trying to figure out how to get it back and doesn't yet understand that he's not going to get it back. This is a hard thing for a teenager.
