How do I let go of a toxic person?

There was this one guy who had a crush on me and i was kinda interested in him too. We talked chated and then slowly i realise he was a narcissistic person. He used to insult me (maybe it was just for fun too but i didn't like it) called me names. Then one day he asked me out and i rejected him i told him i wasn't interested (just to see how he would react because i already have doubt about his behavior), then his anger bursted out and insulted me then we fought and then we cut off each other. But on the other side i have fallen for him too. So im still trying to get him out of my head. Still i feel like its my fault that i rejected him but if he reacted nicely i was about to tell him that i was just kidding and told him about my feelings. But how he reacted was just not expected. Did i take the right decision by rejecting him?
How do I let go of a toxic person?
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