how do you let go of someone?

i have a hard time letting go of people unless they've done the absolutely worst fucking thing ever, then my heart and brain immediately detaches from them without effort, it's like they don't exist. but in this situation, it's just an annoying boy playing around with my feelings, and i want to let go of him and cut him off completely, but i find it so hard not to think about him or not want to speak to him because he hasn't done anything horribly bad outside of being confusing. idk. how do y'all let go of people when you know you need to remove yourself from a situation that isn't serving you?