Why would someone friend zone you then get upset when you reject their offer?

Long story short I will not get into too much details it's too much of a long story but my ex decided that he no longer wants to be with me after 8 years of knowing and sleeping with each other and he also confessed that I wasn't his type of girl and that he was never sexually attracted to me and that he never felt the same way about me as I did for him and said to just be friends instead despite me pouring my heart out and confessing my love for him and he knew that but then when I decided to put my foot down and said that I will not take upon his offer a friendship, he proceeded to Gaslight me and call me "selfish" and basically a narcissist and telling me that "it's all about what I want" and being upset with me that I don't want to be friends with someone that I have fallen in love with while he goes on and fuck other women.

But I have also heard other stories of people friendzoning someone that they do not have romantic feelings for and then getting upset when they finally move on why is that? And why do people expect someone to be friends with someone that they know have feelings for them and want to date and yet call it selfish when they refuse to and decides to move on instead? Doesn't that sound like entitlement?
Why would someone friend zone you then get upset when you reject their offer?
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