For me, sometimes going "cold turkey" is best. I happen to love fruit flavors esepcially lemon so you might try eating hard (sour or not) candies in place of a piece chocolate. Most have fewer calories piece for piece. Then you can try weaning off the sweets altogether.
You should also keep a list of how you like the chocolate. If you like chocolate pudding and warm is your thing then maybe having a cup of low cal cocoa would be better - just changing up the chocolate itself by texture. For instance, there are healthier chocolate treats like cereal with chocolate soy milk.
I also find that certain times of day are triggers so I plan another "treat" which might be diet Jello as a parfait with low cal Cool Whip on top and sprinkled with chopped nuts, bits of fruit, or dried coconut.
You may need to use different strategies at different times until your palate has changed.
I just gave up artificial sweetners including diet soda. Instead of one per day, I cut back to one a week. Now I drink plain ice tea especially out. It took about a week and I just made up my mind I was stubborn enough to do it. You can, too. Good luck!