Why won't my ex let me go?

He's in love with someone else but wants to be friends with me.
I think my ex is the avoidant type
Whenever I stay quiet, he just watches when I enter the messaging app, and he sends maybe one or two text messages asking if I'm ok.
He doesn't do anything else until I open the app again and maybe after a few weeks, repeat
Why won't my ex let me go?
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