Addict is right, because your behavior reminds of people with alcohol and drug problems. They want to quit, they know they need to quit, but just can't. Or they quit for a while and then they think, okay, one drink won't kill me, so they have one. Then the next day they have two. By the next week they're up to four and five a day, and before you know it, they're back in full-blown, out-of-control addiction.
In your case, friendship is your attempt at moderation; your "one drink" is thinking you and Bad Boy can be friends and remain that way. Clearly, you cannot. You two might keep your paws off each other for a while, but sooner or later you're back to your old tricks, then you end up hating yourselves for crossing that line again -- just like a drunk who wanted to have one drink every now and then but ends up back in jail being wooed by an oversized, cracked-out tranny named Diamond.
Every recovering addict knows there's only one way to quit: cold turkey. For you that means making a clean break from this guy once and for all, and moving on with your life. You two cannot be friends. At all. Most couples can't -- there's just too much history and baggage. You are no exception. Until you remove yourselves completely from each other's lives, this same pattern of behavior will repeat over and over and over again. Half-measures will avail you nothing.
Cut the cord once and for all. It won't be easy -- quitting an addiction never is -- but it's the best thing for both of you in the long run. I see no other way out of this self-defeating spiral.