Keep your girlfriend happy. One of the keys to a successful relationship is keeping things fresh in the bedroom. It's really easy for your sex life to stagnate over time, which can cause other parts of your life to suffer significantly. You want to have an open mind and communicate with your partner about the things you like and dislike. Experimentation is basically a must if you want to have a healthy sex life. You obviously don't want to make your girlfriend do anything they don't want to, but if they're willing, it's worth trying anything once. You might find you're into something you never would have imagined.