see the question has never ever ever been and never ever should be "does she like me"
it should be "Do I like her?"
if you do, say so.
otherwise you'll set yourself up for years of being "that friend who couldn't say how he really felt"
""""""""" extra quotation marks for you to apply as you see fit.
no seriously, it doesn't matter if she likes you or not, you like her, and until you can come to grips with that and admit it without shame TO HER, then you're going to constantly justify putting the ball in her court.
You're young so, whatever, consider it a learning experience waiting to happen.
it's not that hard, and if anything she'll take it as a compliment and be flattered and politely turn you down if she values you only as a friend.
In the very least, if she's faithful to her boyfriend, you'll be on her radar when that relationship goes bad. It's not a bad place to be, just don't wait around waiting for him to screw it up, you have some experiences to go through.