“Come on! It wasn’t a big deal. That’s why I didn’t tell you.”
When a cheater responds this way, they are engaging in gas-lighting. Let me explain:
They know whatever happened IS a big deal to you. So, they say this to cover for themselves and invalidate your feelings.
Also, the chances are good that they understood whatever they did was a big deal and chose to lie by omission as opposed to face the consequences of upsetting you.
Personally, I do not buy the idea that cheaters are ignorant of the moral bankruptcy of their behavior.
Why bother lying and hiding the behavior if it is so morally neutral?! And why do cheaters get so upset about faithful spouses exposing the truth of their infidelity if they are so ignorant about it being wrong?!