"I'm the best he/she could ever have."
Really? You really believe that there is literally 'nobody' who could be a better person for them, than you, on earth? added with the fact that you would've wished them the world even if it didn't include you, if you really were the best they could ever have. They did sth wrong, sure, but this, your spite, your desire to see them miserable, is not love.
I'm sorry but they're surely better off without you.