Most Helpful Guy
You need to tell him how you feel. If he doesn't understand put him in your shoes, but don't mistreat him he's a human being. You need to make him feel how you feel so if he ends up with someone else he realizes how to treat her/him.
Most Helpful Girl
Just break up with him, he'll realize it later. Bad people don't have good relationships because of how they are so when they finally meet someone who treats them well they don't know what to do with it and act the only way they know how. After you break up with him (hopefully in a nondramatic way) he will realize what he lost down the line and could probably return in the future if you were good to him. You don't need to have an impactful breakup