Here's your story. Here's the ending.

He shifts slightly, stretching out his body and slowly realizing where he is. His dark uniform is damp from the humid air created by the waterfall and the girl laying next to him is soundly asleep. With his stealth, he moves to the mouth of the cave, scanning the area through the waterfall. Suddenly, he crumples to the ground, gripping his bleeding chest. His hand finds a small sleek knife with a silver handle sunken into his heart. He grunts and finally yells out in pain, startling the girl. She jumps to her feet, running over to him. He breathes rapidly, his heart failing. His hand shakily reaches towards the girls face as she kneels beside him and caresses her face. He guides her head down slowly to his and kisses her weakly before losing his life. The girl is sobbing, looking over the man's body and slowly takes the knife out from his chest. She sets the knife aside and removes the mask from him, seeing his true self. She cries uncontrollably until she grabs the knife and his mask, walking through the misty waterfall, with her face dripping with tears but her heart as hard as stone.