He follows me but won’t message me?

This guy hasn’t contacted me since 5 months ago. During those 5 months he has been following me. He works near my neighborhood and when he sees me on the freeway, instead of taking the exit to go to his work, he follows my car. Sometimes he drives behind me, next to my car looking in my rear mirror. There was one time when he was in the car with his friend, his friend was driving, and he pointed at my car, and the friend followed me.
I sent him a message saying hi the other day, he saw it but didn’t reply.
I don’t get it, why is he doing that but won’t contact me?
He follows me but won’t message me?
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