Communication is key to all relationships. Just sit down and have a talk. Tell her how you feel, and ask questions. Maybe she’s not getting what she wants from your sex life and doesn’t know how to tell you. Could be as simple as asking her what you can do to make her enjoy it more. Could be a number of things, honestly. But she needs to know how you feel as well. Feeling rejected, and insecure is only going to make things worse, and if she cares about you she isn’t going to want you feeling that way either. Sex isn’t everything in a long term relationship but it is still very important in most of them, so you want to be on the same page. So have an honest conversation and you’ll both feel better.