Why does my ex feel the need to explain himself?

So my ex broke up with me. Before we broke up we spent a lot of time together (the split was because he felt I took up a lot of his time). Since then I've been doing my own thing and he has been doing his, but from some reason he needs to explain stuff to me.

For example, I'll IM him something at 3pm and he'll answer it at 8pm with a reason why he couldn't reply. Also, he always tells me goodnight (sometimes twice. and might even text my phone with it) or if I'm playing games online he'll want to join. He has also been a lot angrier than usual (not at me, just in general).

I've already explained to him that I'll move on since he doesn't want a relationship..but he kind of acts he owes me something.

So confused.
Why does my ex feel the need to explain himself?
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