I [15/M] am in a relationship with a girl [15/f] and I've gotten into a strange position, involving another girl [16/F].

First off I would like to say, Yes I know I'm only 15 and this shouldn't be such a big deal, and I agree, but I mostly don't want to hurt anyone else involved, so lets push that aside for a second.

For the longest time, I used to like a girl, Let's call her "A." She was literally everything I wanted in a girl, right down to being a redditor. I was crazy about this girl, but she seemed to have little interest in me, beyond being good friends. Time passes (Quite a bit of time, mind you) and I've finally accepted that she doesn't like me and moved on.

A while later I start to hang out with a new girl, we'll call her "K." I have hung out with her before but was never very close, until this time. For some reason we just clicked and we started to hang out with each other every day. One day, some time later, I have a party at my house (A school related party, nothing crazy) and me and her talk the whole time. At this point I began to realize that I liked her.

So I talk to a close friend of mine (Who happened to be dating her best friend) and told him about it all. He then tells his girlfriend to talk to K. about me and see what she thinks. Turns out K. really likes me, and so naturally I'mm very excited. A month or so passes and we end up dating, very happily.

Then one night I receive a huge text from A. explaining how much she likes me and thinks I'm the most amazing person she's met.

Fuck.

So I basically told her everything, that I liked her, and that I moved on and started dating K. She's surprisingly okay with everything (or at least she says she is, i'm more than sure she isn't.) A bit more time passes and I think that everything is perfect because I'm happy with K.

Recently though, (Me and K. have been dating for a month or two now) I've been starting to notice certain things about K. Don't get me wrong, she's fantastic, there's just one thing about her that makes me question everything.

She's very childish. For example, when we're out in public, I'll turn around and she'll be off messing with something or running around somewhere. At first it didn't seem so bad, she was just a playful person, but it gets more and more annoying. For example, we were in the band hall of our school, and i noticed she wasn't with me (that's when the "oh shit" feeling comes over me) and then i see her across the room with a mallet banging one of the really big drums. I almost died of embarrassment (neither of us are in band)

When we're out I feel like I have to be holding her hand or she'll go and break something, which is definitely not the way you want to feel about your girlfriend. It's as if I'm half dating her and half babysitting her.

And I can't help but think that I would be more okay with it if I didn't know that A. (Who deep down I know would be a better girlfriend) didn't like me. I feel like a horrible person breaking it off with K. just because she's a little hyper, but then I don't want to wait too long so that it will just be harder in the future.

So what say you? Should i accept the situation and make it work with K., or should I just move on and hope that sometime in the future I can get with A.?

Sorry for the huge wall of text...

TL;DR - Liked one girl a LOT, got over her, got into a relationship and it turned out the first girl actually liked me. Now my relationship isn't going well. What do?