Please help! I don't want to lose interest in my girlfriend!

I have a good looking girlfriend (18) who is super into me (22), faithful, funny and always wants me to be happy. Her family and friends all love me and my family loves her. But for some reason lately I just haven't been feeling the same for her. Yet, I can't bring myself to break up with her! I keep thinking about what a huge mistake it would be to break up with her and undo everything we worked for. It also makes me depressed to think of us not being together. We've been together for a year and five months. How do I rekindle the flame? I want to be attracted and love her like I did before. Should I give myself some space? I need solutions, please help!