Went on a date. He rejected me and now he's acting weird?

So this guy that's observed me in class for a while confessed that he liked me and asked me out.
We went on the date and when he dropped me off home he kissed me.

I was shocked as it was my first kiss and it kind of showed on my face but I just got out of the car.

Two days later he says he's too busy to date but enjoyed it. I told him that's fine and that we can just be friends.

Now when I bump into him he avoids eye contact with me and when there's someone with me, he'll pretend I'm not there and pay all his attention on them.

I don't know why he's acting like this. I sent him a message to show that we can talk. He responded nicely but ended the conversation
Went on a date. He rejected me and now he's acting weird?
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