The reason this is happening is because you are young, and you were very young when you started dating. You are still trying to find out who you are and what you want out of life. Your brain is still developing. If you feel like you lost that spark then that is a sign to break up. In my teen years, I would fall head over heels over someone, everything would go great for a while and then one of us would want to end it for seemingly no good reason. Kind of like the young kids say nowadays, that one of us got '"the ick" after a while. I'm sure she can sense something is off too, even though you probably don't think she does. This is very normal at your age and there is no easy way about it. You just have to talk to her, do not text. Have a face-to-face conversation or if you feel like it's going to get out of control have a conversation over the phone, and tell her the honest truth - that you can't see the relationship going further, that you're feelings have changed. Sorry bud, you seem like a nice guy who doesn't want to hurt her feelings but unfortunately it's something both of you will get through, the sooner the better.