I find it hard to let go of a guy I've been seeing on and off for 2 half years. He treats me badly but I can't let go. What should I do?

The short and easy answer is to let him go. The thing is that someone that does not treat you right does not deserve you, regardless of who you are. Stop seeing him, block him on social media, clearly tell him to go , do whatever it takes to get him off... You deserve someone that treats you right. Keep looking, this relationship may be a failure, but it takes one to know one and you can't succeed without these. At the end of the day, keep in mind that he is the problem, not you. Go get yourself the best :)