I've been put in a strange situation and I don't know what to do?

I've had my eye on this girl since we were 14 but I never did anything because A. I'm a ***** and B. I've always understood that she wasn't after a boyfriend. Now we're 18 and she's known I've liked her for pretty much the whole time but we are really good friends. About a month ago I'd finally plucked up the courage to ask her out to go to see a comedian with tickets I got for my birthday but that same day she told me she had a boyfriend from outside of school which obviously surprised me (as per what I said earlier) and made me think that all my chances were over. But now ever since then she has been giving me a lot of the signs of her being interested, especillay last night which was our 6th form leavers ball, which she has never done before, even publicly on Facebook, which her boyfriend can surely see, which is the last thing I would do e.g. her profile picture is of me with my arm around her that we had taken at the ball. She has been saying things like "I'm only really with him because he's hot, he's quite boring really, he doesn't make me laugh like you do" I don't how much she meant that and it was at the beginning of the relationship so she might have warmed to him a bit more since then. I don't really understand what's going on or what I should do and I was wondering if someone here could help me? I still want to ask her out but I really value our friendship and I don't want to ruin what we do have

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