Ignored my messages but stalks me?

Why would someone do this? I found out he had a girlfriend after years of talking to him and he made it seem as tho that was the end of the conversation. He ignored me for at least 2 months now and it hurt really bad but I've accepted it and continued to live my life. Deleted him on all my socials but yesterday I posted a snap story and out of no where I see that he watched them. And I know he knows I have a Twitter account to so he's prob stalking that as well, I just have a strong feeling of being watched.
Ignored my messages but stalks me?
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