Breaking up with a sociopath is admittedly hard for both the target and the sociopath. Many people say the best way is to go cold turkey and cut off all contact. That is the quickest way. If quickest always means best in your mind, then I guess it would also be the best way. Depending on your sociopath, though, it might feel more like breaking off a thumb to free yourself from handcuffs than ripping off a band-aid.
The truth is that you and your sociopath have formed a symbiotic relationship. You may think you owe him nothing, but the relationship matters to the sociopath in ways you cannot guess or understand. You may think the sociopath respects your boundaries, but the sociopath will not be sympathetic to your assertions of your needs. The sociopath does not have or respect boundaries. The sociopath has his needs, too, and will fight to make sure that they are met. You do not want to get into an all-out fight with a sociopath when the sociopath feels like his survival is threatened. You will lose.
With a sociopath, the best thing to do is to make the breakup seem like it was his or her choice. Like with ticks or other parasites, you want to poison the well so the sociopath willingly leaves. Become a helpless, emotionless, reactionless burden. Start being contrary, without being openly defiant. If the sociopath likes to go out, develop a preference for staying in. Stop bathing. Focus on work. Pretend you're tired, sick, depressed, say you forgot your keys, you forgot to feed the goldfish, be incompetent but make everything seem like an accident. If the sociopath gets mad, say sorry, but don't fight back. Say "I don't know what's come over me." Have long phone conversations with your mother or other people the sociopath hates. In general, let yourself go completely and be as intolerable to live with as possible without being confrontational. This may seem very passive-aggressive, but after about three months (give or take), the sociopath will be out of your life. You should be in the clear after your sociopath has been gone three to six months. By that time the sociopath will not need you to satisfy any of his basic needs, and will see you instead for what you really are--probably a weak-willed whining sissy.
Think this is unnecessarily complicated and time-intensive? I suggest you watch Sleeping with the Enemy and let me know if you think there are better alternatives.