Why is he pissed if he doesn’t like me?

So I’m crushing on a guy who treats me like shit. Doesn’t take me serious and makes fun of me behind my back. However he brags to everyone about how much I like him and he acts like he owns me in front of his friends. Well one of his best friends, his closes friend who’s been friends for many years did something. He went behind my crush’s back and tried to talk to me many times. My crush finally caught him trying to talk to me and got extremely angry and cursed him out.(His best friend knows he treats me like shit) They aren’t friends anymore and now my crush doesn’t trust anyone. I’m not his girlfriend so why is he so angry at his friend?
Why is he pissed if he doesn’t like me?
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