I broke up with my girlfriend. Why do I feel so awful?

A little background info:

We're juniors in high school. (Don't take this the wrong way and look at us as immature people, because we're definitely on the mature side of the spectrum). We dated for six months. We texted every day from good morning to good night. Hung out once or twice a week, plus weekends. We got along great with each others friends, and never fought once. She was really amazing for me. But about 3 weeks ago I started to lose feelings for her, and I couldn't understand why. I just felt not as interested in talking to her and what not, and it was really affecting me. But she never did anything wrong at all, so I knew if we broke up, I didn't wanna hurt her, if anything.

She would always tell me how much she liked me and how much of a positive difference I had on her school year, how she's never been happier with someone, never thought she would date in high school but I proved her wrong, all that. And i could tell that she was absolutely genuine about it. So knowing how much she liked me, it was difficult to bring myself to end things, but she noticed something was wrong, and we ended up talking about it because I knew that the truth was better than leading her on in a relationship where I didn't like her as much as she liked me.

We met in person and talked it over and ended it. She stayed pretty composed, but I felt awful because I could sense how much she was hurting.

I've been really upset and confused since it happened, I know I hurt her a lot, and it tears me up inside to see that because she's such an amazing person. So now i've been hit with all these emotions, I'm not sure whether I regret it, want her back, miss her, think it was the right choice; its all a huge mess. But I've felt horrible and I don't know if it's simply because I feel bad for her, or if I made a mistake.

Please help, anyone.