Why my Japanese boyfriend always silent when he's angry?

Tbh I'm the one who got angry because he couldn't let me know when he's busy , I only need 1 message from him to let me know when he's busy so I don't have to texting or calling him "where are you what are you doing?" But he always forgot.. and it makes me upset.. he said sorry, but he always say sorry anyway but still forgot.. I only asked one thing but he always forgot.. I don't want to keep telling him to do this and that, I'm also busy but I always let him know.. he's silent till now, it's been a day, what should I do?
Why my Japanese boyfriend always silent when he's angry?
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