My friend's girlfriend just admitted that she has had feelings for me since Sec-1

I am so messed up right know.But, please,bear with me.
I'm in Sec-4 right know and my (not too close) has been dating a girl,
a best friend of mine.We've known each other since Sec-1.The guy she's been dating ; i've only known him for about a year.They've been dating for the past year or so.Anyway,i had just(an hour agao)went up to her house to get my books.

i was about to head out of the door after getting them but she grabbed my hand and she told me to stay and hang out for a while. i agreed,we chilled for about 2 hrs or so.we had been on the sofa watching a rerun of a DADS episode and she had grabbed my hand and been playing with it.I said nothing as things were casual and flirty between us but we had never gone far with it.

But it was starting to get uncomfortable and i started to slowy slip my hand away.i was halfway through bit then she had a viper grip on my hand.She said michael(my name) i looking nervously at the TV screen,sweating like crazy looked up right smack dab into her eyes and she was close ,very close
I was shaking by then.She blurted out that she loved me, had since Sec-1 and kissed me
She drew away and ran out if the room

So here i am in their backyard .PLEASE HELP.I REALLY NEED ADVICE

She has a bf so forget it. Dont be a fool

WTF are you doing in her backyard?

If you feel the same way tell her, but also tell her you will not take this any further unless she gets rid of the BF. It's pretty straight forward.

If she really likes you she will break up with her boyfriend to be with you. If not she wants you to be the guy on the side, never settle for that crap.