Lots of alcoholics (not all) start out as "functional." In fact, as my alcoholism progressed, I continued to maintain my career and professional license, never got a dwi, never damaged my credit rating, owned my house, car, etc. But believe me, I was unravelling inside, and it would only have been a matter of time before my luck ran out or I made some huge, irreversible mistake.
One thing, though--you talk about how perhaps you should have "accepted" his addiction. In fact, that's exactly what you DO have to do. Accepting it doesn't mean that it's OK, or that you should live with it, but rather accepting the FACT of it, and then deciding what YOU need to do for YOUR life to look the way you want it to.
In short, no, you did not overreact. You undoubtedly spared yourself a whole lot of agony by leaving when you did.