Why did my crush crush look at me while talking to another girl?

He's my crush and I seem to be his one (no time to explain it all but it just seems obvious), even though some days he confuses me.
Today, I was sitting with my friends, searching for something in my bag when he walked past me, followed by his friends behind.
I noticed him because I looked up when he was walking in front of me (his back turned) and I saw he was talking to a girl who is in his class. I've seen her before, when he says 'hi' to her for example or another time on his fb profile, they took a photo together.

I stared at him, or more precisely at his back, he turned his head, looked at his friends behind him and then glanced at me.

I don't know if it means anything, but I felt bad this day, he was in his 'ignoring' time (well, some days he can't stop staring and the next he doesn't even look).

Do you think it means something? If yes, what?
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sorry, I wrote crush twice x)
Why did my crush crush look at me while talking to another girl?
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