I have re-read your post after several people have replied and upon the second reading noticed how incredibly tentative you sound. You TRY to end it. You SAY it's over. You need to act matter-of-factly and decisively. Over means over and does not invite any input from him, such as his repeated lame attempts at convincing you that he cares.

I concur with Rose - he is not using you for sex as sex is easy to get elsewhere. He is using you for the advantage he has being with a woman who cares very much for him while he doesn't reciprocate her feelings. He is very clear about it because he calls it fun. For him, it is indeed fun. For you, it is emotional pain and for him, it is fun.

If it is difficult for you to make a decisive move, change your environment to promote the desired behavior. If he has a key to your home, change the lock: if you communicate via a messaging app, block his account. If you respond well to ritualistic cues, collect the mementos of the relationship, if any, and get rid of them. Fill your calendar with events during the times you would typically see him: you can go to the library, for a walk, take a class, attend a meetup, volunteer, meet an acquaintance for coffee, anything as long as it takes you out of the home where you used to have those painful rendezvous with him.