Why do guys go silent during an argument?

I've been dating my boyfriend for almost a year and we have a great relationship overall. He's a great guy but there's thing he does that I don't like... Whenever we argue, after a while, he goes completely silent, either for a couple of hours or sometimes for the rest of the day.

At first I would try to reach him but it was impossible. After he came back to me, we'd solve our problem and I would bring this up. I would tell him how hurt I feel whenever he does this. He said he would try to change it but if anything he only gives very short answers here and there and then goes silent again.

He's a very supportive guy, very loving and we rarely argue (on average, maybe once or twice a month max) and we never raise our voice or insult each other, but like I said, it hurts when this happens so guys, I need your opinion on this. Why does it happen? Is there a way to avoid it? Thank you!
Why do guys go silent during an argument?
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