Two things 1. tell her how you feel. Don't go through life saying "what if?" 2.If she is truly happy with who she is with, try to be happy for her. No its not easy.

That's a good answer. Tell her. If she says she can't be with you, then let her know you'll still be her friend and support her relationship. And yeah, it sucks. But that's okay, time heals all wounds, and you'll probably have a better friend out of it anyway.

I wouldn't let her know. I think you'd feel guilty if by telling her that either caused you and her to drift apart or her and her boyfriend broke up because of you. There's a good chance that at her age, she won't be with him forever, and if they aren't you'll have your chance to tell her. For now just be there for her, don't wreck the good friendship.

Check this out: http://imgs.xkcd.com/comics/friends.png

You'd just be causing her heartache by telling her now. Wait until the time is right. If it's meant to be then the right opportunity will present itself.

Tell her, but DON'T TELL HER NOW! OMG, I can't believe these other answers. Look, telling a girl how you feel is like shooting a target, and you want to make sure it's a hit. For now, I'm sorry, but you're gonna have to deal with that other somebody. What you can work on now, is how to get out of the "friend zone", but don't over do it, cuz she's in a relationship. There are plenty of articles online that can help you with getting out of the friend zone, but remember that she still has a bf, that's IMPORTANT. Once they break up (if they break up, 17 seems a much bolder age than 13,so it could take a while since they've been together for 7 months already) make your move. And this is important. Don't lay all the cards out on the table at once. Telling her how you feel too early in the game will make you appear unattractive. Girls will argue, but believe me, that's wussy behavior, and girls like a challange and they don't like a wuss. You might not understand now, but it will make sense in the long run, bud. This is how you ask her out. Do it in person, in a semi-private place. IN PERSON! And then all you have to say is this: "I really enjoy your company. Would you like to get some coffee with me (or anything of that nature, such as a walk, but not dinner yet though) this Friday?" After talking about that park, or coffee shop, or something, make it obvious that you want it to be a date. Eye contact is key. AND THAT'S IT! DO NOT, I repeat, DO NOT TELL HER YOU LIKE HER JUST YET. Asking her out is already a bunch of meanings packed into one phrase. It means that you like her (obviously), are willing to pursue her romantically, and are willing to put time and money into the relationship. Those indirect meanings are enough, so whatever you do, don't say that; "I really really like you, do you wanna be my gf?", because then she knows that she already has you, and that's how you could most likely fuck yourself over. Back to the challenge part. If she already knows that you LOVE her, then she might feel bad, it might hurt her, and most likely will, although there might be a chance she won't. Girls don't function like us guys. They need time to feel love for a guy. Us guys usually are in love with our girlfriends on the first date or sometimes even before. Saying I lOVE YOU too early will put her into the awkward position of choosing to run away from you, or to be with you. So give it some time before you say those words, but I think that's the least of your problems now. What's important now is to get out of the friend zone and to work on how you can make her be more attracted to you. If you feel the wind behind your back then ask her out even if she's with that jackass, like after they get in a fight or something. That's how I got my 2nd gf. I asked her out and she ditched her bf of more than a year for me! But I'd strongly advise you to wait until they break up, because with that question on Answerbag you don't seem too experienced with dating and the ladies, no offence intended. Don't take her out on a big date just yet. Even if she is your friend, and have known her, treat her like someone you met at the book store. Your first date should be a simple walk or just some coffee. That's it. I'm no hitch, but there's sooo many things I'd like to tell you from my own experience but unfortunately that's all I have to say now. Good luck! And let us now on this site how it went (if you are to ask her out in the future that is)!

If i was you i wouldnt tell her while she is still seeing this other guy if shes as happy as you say she is it may cause alot of trouble for you both and its not fair on her partner,wait untill she is single again and then go for it other wise you may loose your best friend.

Trust me Ive totally been there before. I think the best thing you can do is just be there for her for now, be a friend, and try not to cast those vibes of arousal. Girls can pick up on that right away, she could lose her faith and trust in you. Especially while shes still seeing this other guy. But dont let your feelings for her and her happiness make you feel like you have do distance yourself from her. Oh and try not to involve yourself with her relationship unless she asks your advice. Getting nosy can easily look like jealousy. (They can pick up on jealousy too) Sometimes the jealousy is flatering, but other times it makes one look selfish and possesive. While your speeking to her, always be enthusiastic and confident. Say things to her like you mean them. Just be faithful, fun, and friendly with her and you might be the one she turns to should things go south with this other dude. You showed definetly let her know that your happy for her when ever shes happy. Even if it somtimes may hurt. But if you love something, let it free, and she doesnt comeback it just wasnt meant to be. Good luck!