Why did he block my messages, but still stares at me excessively?

A guy friend and I had a flirtatious relationship, in which we later decided that we wanted to do more, however I found out that he was talking to different girls and kinda angrily told him "No thanks" to the relationship, but we could still be friends. Yet, sometimes he speak to me (very low though), he sometimes goes out of his way to be around me and I catch him everyday staring at me excessively--he watches me walk by or down the halls, but when I look up at him he puts he stares away. Anywho I tried sending him a message on Facebook about our friendship, but I discovered that he blocked me on Messenger. I basically would like to know, why would he continuously stare at me but block my messages? What does it mean? Please help me out. Thanks for everything.
Why did he block my messages, but still stares at me excessively?
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