What his behavior mean?

There is this guy that I liked before who has a weird behavior towards me.
2 years ago we worked together and we start to became friend, he always touched my arms, my thighs, he always joked with me ecc, with the passing of time he started to give me less attention, but it wasn't a problem for me. Now we don't talk anymore but when I go out with friends I can see that he stares at me. This behavior make me really angry because I don't understand why he stares at me...

In your opinion why he has this behavior?
What his behavior mean?
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