Why did he suddenly reject me?

He told me after we had been dating for a month that he liked me and he started to make plans for the future with me. He texted me a lot and was much more into me than I was into him. He told me, a week after he told me that he liked me, that he dont like me in a romantic way and dont want to see me anymore. He told me this after i told him that I want to date exclusive. I dont understand what happened? Did I scared him?
Why did he suddenly reject me?
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