why is my crush ignoring me?

I like him. Andb he knows I like him. Also I know he likes me. We flirt all the time in class non stop. Yesterday we flirted alot, and today he hasn't said 1 word to me.... i caught him looking at me in the corner of me eye a lot. And 1 time we looked at each other it was awkward. I just want to know why he ignored me today but looked at me. I am so confused we always talk. It doesn't make sense to me at all. Also in the hall ways when we each other at school he said hi a few times and stares alot. But latley he has been not saying hi. And just looking at me its weird. Please help.