How can I (23M) break up with my fiancé (22F)?

My fiancé and I have been together since high school (about 5 1/2 years) and things seem to not be the same anymore. I feel like I'm ready for a different situation (geographically and physically). The thing is, I love her so much and can't bare the thought of hurting her, but I just can't shake the feeling of wanting to exit. I find myself getting upset or annoying if she's sad or upset and I kind of shut down. We have been living together for a while now and even started planning a wedding. She's completely unaware of how I'm feeling because I've just kind of been scared and waiting for it to get better but it's not. I need help on how I can break things off. Anything will help, thank you!