I feel trapped and tired of pretending.
Why do you think you feel like you are trapped?
I just feel like I can't break up with my girlfriend.
It's understandable to feel that way, but you should end your relationship if you feel trapped. It isn't healthy to stay in a situation that you dislike being in. I think you should talk to your girlfriend and tell her that you need to break up.
She probably deserves better and I have to let her go.
Feeling trapped in a relationship is a terrible feeling. If you want to leave your partner you are better off doing it sooner than later. This may be difficult, but it will be worth it in the long run for your happiness.