I had this topic come up and I couldn't figure out which would be worse. And I'm sure its also varies a lot for men vs women.

On one hand, being cheated on, probably the worst act of betrayal you could experience, the love of your life is no longer the one you fell in love with. Whereas on the other hand, you find out the person you fell in love with was NEVER who they portrayed themselves as nor who they were in your mind, and your WHOLE relationship was a lie.

Also keep in mind the severity of the partners hidden past, and the depth of cheating can vary a lot, they could have cheated as little as just flirting with someone else, and they could have a hidden past even as severe as having been a prostitute who had kids that they gave away for adoption (could even be non sexual, like they use to be in KKK and lynch people of colour or somethin). So comparing one example to another may not be fair.

I'm guessing women will say finding out about your partners hidden past is not as traumatic, they're still the same person and loves you. Though consider that they had to use deception and manipulation in order to get into a relationship with you. Whether or not you would have stayed if you knew before is irrelevant, because they didn't give you that choice, and instead manipulated you. And if they manipulated and lied about this, then what else have they been doing? It really does destroy the whole relationship as well.