I really want to say good bye, but I want to know how to word it all right?

Long story short I want to say good bye to some one who I kind of let walk all over me but I wanna be the bigger person here make it a good bye instead of argue and fight so I don't feel bad at the end of the day.. This guy has done messed up things to me in the past but now he's better but I'm realizin it's time to grow up and just because he walked into my life doesn't mean he has to be here forever.. Any ideas on how to word it or tell him goodbye in a civil way?