Why does my ex dm me that he feels bad about how things left off but doesn’t text back when I answer him?

I’m not sure what he’s trying to do or he’s embarrassed or acts impulsive? he randomly dms me “i just feel bad about things left off. just been on my mind lately” and i answered with “?” and he never answered me since then. by the way this happened in Feb and to this day, he would randomly add me on snapchat (M18 & F19), like my instagram story, unfollow me and follow me back (i do not follow him back anymore). What is this behavior?

Why does my ex dm me that he feels bad about how things left off but doesn’t text back when I answer him?
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