She's gone, and he can't believe it. This is inconceivable to him. Never in his worst nightmares has this ever occurred. She's been such a key part of his life for so long. He can't even remember what life was like before she was in it. Oh, yes he does. It was gray, bleak, meaningless. It's like his life began when he met her.
But now she's been lost to Death, and he's not sure what to do anymore. All he really wants to do is fling himself off the roof of the tallest nearest building, but he doesn't want to cause even more suffering. She's already done enough damage.
So he sits and cries. That's it. Sits in his pitch-black room, special black-out curtains on his windows, and cries. He hasn't eaten in days, hasn't bathed in days, hasn't been out of his room in days, hasn't seen anyone in days. He doesn't really care. She's all he's ever wanted and her passing has basically killed him.
He has nothing to live for anymore. He can't really stand his family (though he loves his parents), and he doesn't have many close friends (except her brother and her cousin). So why should he make an effort anymore? He shouldn't have to, so he doesn't.
And that's how he dies. Mourning a lost love. What a tragic ending to a tragic story. But then they are together, and everyone knows that he and she are happy now. So they don't mourn him – not exactly. They give him and her a joint funeral. But it's more of a celebration of life and love than anything else. And everyone smiles as they cry, because they know that's how she and he would want it.