Why did my boyfriend flinch when he said this?

So the other day my long distance boyfriend was home alone and he went to bed early and then woke up and said ‘right better get back to bed’ and then I questioned his actions that day and why he didn’t seem to be communicating with me and then he said ‘why are you so bothered it’s not like I was messing around with somebody else’ and then he flinched when he said this and his facial expression changed

Why did he flinch and his face expression change when he told me that?

Why did my boyfriend flinch when he said this?
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