Don't worry, addiction isn't something that just "happens" without your knowledge (I mean in some cases I am sure "ignorance is bliss" has gotten people in more trouble than they need to be in), but cocaine is even lacking the dependence aspect of addiction... so you would know. You would have already bought an eight ball haha.
Also, not sure where you got the advice to use cocaine to take the edge off of MDMA comedowns? Cocaine will just exacerbate every single part of the MDMA comedown. Food, sleep, vitamins, sex, some kind of downer (as long as you don't have a history of abusing them) are things that work. Cocaine took you from slowly coming down to UP and crashing harder than before. So don't worry, you're good!