I am a male PICU nurse, and like yourself, I consider myself rather emotional. When you begin working in the PICU (probably any ICU), you may be affected at first and be overcome with emotions; however, as time progresses and you begin to see more heartache, senseless deaths, child abuse, etc., you become "sensitized" (I did anyway). You never get used to seeing these tragic incidents, but you get to the point where you understand how to handle your emotions. Furthermore, nearly every nurse I work with is "tough". You grow a thick skin working with other nurses, physicians, and unruly families. The biggest problem for me initially was bringing emotions home with me. Even if I grew very close to a child who was dying, when I left the hospital, I had to leave my emotions behind... otherwise your personal life and your family becomes affected.
You are still young and have many years ahead of you before you enter the nursing profession. My advice to you: ENJOY high school, study hard, and learn good study habits. It is great to start considering your future career plans, but enjoy your time before you enter college.