And that's supposed to be a problem???
Even if she did it wouldn't be a bad thing, nor would the male lead even have any rights to judge nor say anything even if he knew.
She was in a relationship, if they did go that far that's on them, it's their private life.
She has no reason to spill that shit out, if she wanted to keep it a secret it's fine.
Right now is what matters, and right now she is single and that past is over.
She didn't do anything wrong.
If someone doesn't like her for this that's personal bias, not any fault on her end.
You absolutely can and will be judged for things you do in life, whether they're right wrong or neutral, it makes no difference. In the first place, something being wrong is entirely subjective.
Anyways, he's clearly jealous and wants to overwrite her experience from the past, obviously.
Also as a side note, personally, I think people who keep secrets from their significant others like that don't tend to have non toxic long lasting relationships. Idk, could be because you shouldn't be keeping secrets from someone you supposedly love, especially things you KNOW they want to know, even if it hurts them. This does not just apply to things you did in the past or body count btw, pretty much anything. I've heard horror stories of a dudes wife hiding her cancer from him and just dying, that's kinda fucked.