Why he doesn't reply my messages, but started to stalk me?

usually we would text almost everyday. but after a few days, I felt weird like I didn't receive any message from him so I texted him several times from time to time , because he still not reply, I decided to delete his contact number which made my picture and my last seen can't be seen. but the next day, I noticed he started to stalk me..
Why he doesn't reply my messages, but started to stalk me?
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