Why would he keep changing the subject?

My boyfriend and I got into a fight where he randomly just started accusing me of cheating on him and we broke up. He later called me to tell me he was joking. I didn’t understand what happened and was trying to get him explain but he was pretending like nothing happened and kept changing the subject. He dumped me to acting like it didn’t happened and refuses to explain anything.

Why would he keep changing the subject?
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