As someone who has been addicted to drugs and alcohol I find it funny when people say they are addicted to stuff like sugar or diet sodas. The jury is out on whether or not diet sodas are harmful for your body.
Keep in mind that there is research showing a correlation with drinking diet sodas and type II diabetes. A correlation, however, cannot show causation. It's more likely that people who are overweight and therefore more prone to diabetes are also more likely to drink diet sodas.
If you were drinking a twelve pack a day I would say that it's time to cut back. Two cans of diet pop a day? Doesn't sound too bad. Remember that animal studies showing that diet soda harms you usually feed the test animals an ungodly amount- say the equivalent of 50 cans of soda a day to "prove" that it causes cancer.
I don't drink diet soda every day but sometimes I will have one with my breakfast in the morning. Is it going to kill me? Probably not. There is a study out there to "prove" that anything you eat, drink, or come into contact with will cause cancer, heart disease, diabetes. Live your life and don't sweat the small stuff. That's how you get screwed up in the head and start restricting too much and bingeing- take it from someone who knows.