Why is my ex is acting childish?

this is a continuation of the other question I have: "Why is my ex acting like this" I sent him a message on fb telling him how childish he was how he's not good enough for me, and all he said was: jkjkkoko

(no joke). and when I posted on his page to leave me alone, he said:lol. I don't understand why he is doing this, he's the one who contacted me first.
Why is my ex is acting childish?
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