Ex boyfriends

Do you girls ever have that one boyfriend that just won’t let your ass go. And know matter what if his in a relationship or not he still bothers you. Well I’m having that problem smh my ex still kept hold on my number after all this year and still be hit me up. Asking me if he can see me and all this other bullshit. Why is it that our ex’s still be hitting us up??is it because they know they messed up a good thing I need to know because I’m confused.