Why is my crush avoiding me?

I worked with a guy for a few weeks (we didn’t work super closely but we saw each other from time to time). Nothing was directly said but I assumed that he had a crush on me because I had one on him and I felt that energy. I felt it was returned the crush sensation.
he then went on vacation for a few weeks. He has returned but hasn’t acknowledged my existence, in fact it seems like he is avoiding me. There have been moments where our eyes could have locked and he could have smiled. Instead he quickly turns away. I notice him twice a day stare at me from afar. But then doesn’t do anything about it. i don’t get it. Wouldn’t he want to find an excuse to engage with me again. A conversation. Even just a smile or hello. Instead it’s been a week and nothing!
was I imaging the returned crush feelings. Was it just on my end?
Why is my crush avoiding me?
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