I don't judge in the sense that it is not my place to tell you whether you are going to heaven or hell...
But if there is one place to make other judgements it is in relationships. This is your life! The number of times something happens to someone in a marriage and you ask, "Did you have any hint of this when you were dating...?" This is the time to say no to someone who bites his nails because you CANNOT exist with someone who does that...even if it seems ridiculous to others. Some things are deal breakers.
This is the time to sort the seeds from the chaff.
So, she has been with this guy for 2 and a half years. In light of this new information what does this mean? Has he been cheating on her? Did he lie about being in love with her? Is he seeing prostitutes? Basically, has he really changed? If she really knows this man, which if she has done her due diligence in 2 years she should, are these really issues or is this the past?
I did not sleep around so it was important for me not to be with someone who sleeps around. Not because it makes me a better person (it does not) but because we were likely to have similar values and similar baggage. If I met and fell in love with a man who had slept around I would have wanted to see him remain celibate for a significant period of time to prove he had changed. Then the past would be the past. But she sounds like she did not ask or care to ask. If it was so important why did she wait so long?
So her big task is whether or not he is a changed man and looking at the past, does this shed light on his behavior in the relationship? What does it say about the future?
If he has changed but she cannot handle his past it is best to end things and make that a priority for her next relationship. And she had better not be pointing fingers at him with skeletons of a similar nature in her closet.