First of all you should think about your expectation. What are your expectations with her? You can not impose your expectations on others. Before complaining about her have you thought about yourself? Are you doing the same thing which you expect with your partner.
Faith and believe are the pillar of every relation. If she is going outside for long then it is not a crime. You should believe her. So my suggestion is that you must be calm down, don’t expect too much with your partner. Treat her like your partner not like a slave. Be nice with her. Think about yourself and your behavior. I hope that if you do this your life become peaceful and full of happiness.
One last thing, you are 19 years old so you must give more priority to your carrier and stable future.