Why did he change so fast?

I was in a friends with benefits and decided to end it bc I am currently talking to someone. I told him that and he said it was a good exscuse, called me a slut and said good luck finding another 6’4” shredded hot guy like me and left. We were friends and the fact he talked like that to me really hurt. Did he not like me or was he just scared of rejection?
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Like I don't know what I’m asking at all. I just need advice and help for not feeling so depressed. I am scared and extremely depressed and need help
Why did he change so fast?
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