Break it off now Son. Don't take this relationship any further. This is only hurting you as well as her bc you do not love her. Put your self in her shoes. Just explain yourself and save her the pain and get out. Plain and simple. Good luck!!
Do her a favor and tell her your feelings NOW!! The sooner you do it the sooner she can get on with her life, the sooner she can find someone who really loves her. You never know...if you've been feeling like this for awhile she may have already picked up on those vibes. Maybe it won't be that much of a shock to her. Just make sure you're not just getting cold feet.