What is a good way to end my story?

My story is about a guy who's sister died a long time ago. He was so upset about it that he kept it a secret from everyone he knew. (Except it mentions later in the story that he told his girlfriend.) When he finds out who the killer actually was, he tries to hunt him down and kill him, but eventually gives up and is so full of grief that he locks himself in his room and never comes out. All his friends are wondering what's wrong with him, and start arguing, blaming random people. Finally the girlfriend gets so mad she blurts out about the guy's sister. Everyone is shocked, not knowing he had a sister, and start feeling really guilty. One girl (who has a huge crush on the guy) gets furious and runs away, angry that he never told her anything about it. All the friends decide to team up and find the killer to make their friend feel better. When they eventually do, they find out that the killer actually killed her on accident, and didn't do it on purpose. The killer bursts into tears and explains that he never really meant to hurt anybody. After that, I really don't know how to end this story. Any suggestions?