I have to disagree with the reply on a number of things. First, the time or if to reveal your past. If he didn't feel secure in telling, then he shouldn't. Obviously it was the right decision as she left him because of it and not from not being told.
Two, the advice to go ahead and talk to her friends should be do it without identifying who she means. Talking to her friends and naming the guys is the same as outing him to everyone.
QuoteClearly he thought you'd find it pertinent; that's why he discreditably withheld it, lest you reject him.
There is no way someone can know what another was thinking. This doesn't belong in a thoughtful and public reply. To me it sounds like he didn't feel ready to disclose his past. The woman doesn't say anything about it progressing to the point of kissing or anything else. Yet the reply is full of assumptions on that point.