Why this behavior?

me and my ex broke up half a year, he always lied to me and was still upset with me when i found out. we ended up badly with him saying that he never wanted to talk to me again and that I hurt him. I never realized how it was possible for him to say this, 1 month ago he sends me a message. After a while he told me that we could not be friends again. What's his? I know it’s not worth my thinking, but I’m curious to know why.
Why this behavior?
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