I think the guy I crushed on in school ruined me
Why do you think he ruined you?
Because I really liked him. But I was so heartlessly rejected by him.
It can feel awful to be rejected but you should just let it be rather than to seek revenge. It will just make you feel worse and people will think you are stuck on the past.
I'll have him feel the same way that I do.
I feel like it's unfair of you to make him feel like how he made you feel just because he's not interested with you. I would suggest that you would get a dating app instead of focusing on people that aren't interested with you.