CP's stupidity is why he, even in the original works, fooled around with a married woman despite controversy. Because of the original Ophelia's craziness, it likely covered his stupidity in the eyes of others since they all had a common enemy. The story was focused on their romance, not his ability to reason.
As for the original FL, it explained why she is the way she is. She thinks her meeting the prince was a fate rightful to her after a life of pain,so she's clinging onto that. It's likely she was always like that but, the same with the CP, it was overshadowed by original Ophelia's erratic behavior.
Anyone can. Her death can happen, seeing as how others aren't afraid of her and disrespects her still. Her husband even needed to put them in their place after the disrespect. I get that he's being pictured as a powerful villainous character but it's also pointed out obviously that he's restricted at some points. Might be because he's technically not the male lead in the original. (〜 ̄△ ̄)〜 Still, vulnerability and cunningly making through things ain't bad.
It's good that she's trying to change her image a bit, seeing how ridiculously negative her reputation is. It's just that she could've gotten a bit of a character, not an unstable one. She seemed sly at some point and suddenly naive and idiotic.
The CP is such a typical idiot that it's quite questionable how he's a main character at some point. He's like an unimportant side character because of how he was behaving. The OG heroine is also suspicious, prolly because she's the same as the FL? a transmigrator or a regressor? Dunno. She's still a cheater and a shameless one. No matter what circumstances you got with your husband, whether separated or not, there's should still be some distance between you and the prince. Weird detail to just brush off. It's like cheating taken lightly.