oh courage I'm sorry this happened to you.
I look at this in another way. C1 is on your side, proud of you and sticking up for you. Saying what a good thing you've done etc and telling C2 they are wrong/out of line for keep trying to bring up your drinking past.
It wasn't said in gossip or maliciously,just a matter of fact thing. I wouldn't say anything. Hold your head high and be mighty proud of yourself. Your colleague is. I'm sure neither colleague mentions it again