How can one be so emotionally immature?

So I've been seeing this guy long distance for quite some time. (We knew each other before doing so) And all of a sudden he stopped communicating about anything that had to do with our relationship. Like he will answer generic questions but ignore everything else. I've already worked through that I need to move on and I don't deserve this behavior, but I can't get past the part where he just started ignoring that aspect of our relationship. And here I am trying to guess what is going on, what happened. This is a grown man (40) with everything else going for him. Like I don't understand. All it took was a tiny explanation. Yes, it would have hurt, but in the long run it would have made sense. I don't understand how to comprehend this type of behavior.
How can one be so emotionally immature?
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