Need advice, getting very mixed signs! (10PTS)?

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I liked this girl, one day she starts to notice me and look back. Later that day she suddenly liked all my Instagram photos, added and invited me to a BBM chat. We start to talk and she gives me her number, we then end up having a great, flirty convo, she made it very clear she liked me, using a whole bunch of emojis too and stuff, ending with "We should do this again , it was great talking to you". Next day she texts first and we get into another convo, although this time I can tell something is different and she doesn't seem to be as into it. So I text her again the day after and again she seems like she doesn't want to talk very much, answering mostly with one word responses. I know somethings up at this point so I try to talk to her in class on the Monday, she seemed totally withdrawn and gave a strong impression she didn't want to talk. I give it a couple days rest and in the mean time she unfollows me on IG and unlikes all my photos, so then I try to text her one more time, she ignores me until I ask her "What gives? I'm confused here" so she asked me what I was confused about and I told her, asked her "what changed?" she says "Idk I just stopped" so I then I try to patch things up and say "Look give me a chance and get to know me" and then asked her if she wanted to go somewhere with me the next day. Thats when she says "Sorry...um but I have a Boyfriend". Haven't seen her a guy yet, and am very conflicted about what I should make of it. Need advice, thanks.
So basically I have no idea what I should do next, don't know if she lied to me or not about having a BF to blow me off, or that she did feels something and someone asked her out right after. Idk. I still have genuine feelings for her and I want to act on those, but I also think I should just walk away and move on. Very conflicted I guess.

The duration of all of this was a week
Won't interfere between them if she's with someone