How do i get rid of him?

sooo my ex and i broke up a year ago, we still act like were dating. but he has "other girls" on the side. i know he loves me the most and he just likes them, but still ? its rediculous. i feel like im on the backburner all the time. he only talks to me when he needs be, even though he says im always first to him. so far ive tried to get rid of him 3 times.. it works for a while but then he comes crawling back and i miss him too so i of course take him. hes had my heart for a year now and he just plays with it. i know its going to hurt but i HAVE to let him go. how should i do this bc we ALWAYS end up gettting back together. what should i say to him next time he talks to me...and when he comes crawiling back?