You are most likely addicted to caffeine and sugar in the Coke. Excess quantities of both are very detrimental to your general health. Sugar can add thousands of calories to your daily intake causing weight gain and leading to diabetes. Stopping your intake abruptly may lead to sugar cravings and to headaches. Substitute it first for DietRite which is both caffeine and sugar ( and aspartame) free, but do it gradually, and than switch to water. Good luck.
Diet or regular? I ask because I used to put sugar in my coffee and over time I found I was putting in more and more. I switched to artificial sweetner, and my use has stayed constant. If you're drinking regular coke, try switching to diet and see if that does the trick.