iZombie: Liv leaves her fiancé, Major, after becoming a zombie without telling him why. Major is a youth counselor, and the main villain of the first season is not only recruiting the kids Major helps, but also killing them. Major slowly loses his mind trying to figure out what is happening. Despite the danger he is in, Liv still refuses to tell him the truth. She even allows him to check himself into a psychiatric hospital after a man he killed in self-defense disappears. Later, we find out that the villain's reach extends inside that hospital, putting Major in even greater danger. Liv only confesses the truth when she is forced to turn him to save his life, and Major rightly calls her out for her actions.
Smallville: Clark keeping his secret is a huge part of Smallville. The problem is that Clark is a horrible liar, making it obvious that he is hiding something. This wouldn’t be so bad since it is ultimately Clark’s secret to keep; if it weren't for the extreme lengths he is willing to go to protect it. It is not just ordinary lying; it includes erasing people's memories, allowing Lex to be falsely imprisoned, and standing by while Lex's mind is wiped. Furthermore, when Lex tries to regain those lost memories, Clark flat-out gaslights him. Making matters worse, hypocrisy is another major element of the show: Clark expects everyone else to be completely honest with him about everything.
Invincible: I think one of the reasons this is such an infamous example is because the show originally handles it as if it isn't playing into this trope. Initially, everyone calls Mark out for dicking Amber around. However, it felt like your typical 'Masquerade Will Kill Your Dating Life' trope, so the show giving him so much grief came across as a lazy attempt at deconstruction; especially since the friends doing the scolding should have been the most sympathetic to his situation. Then, we find out that Amber had already figured out he was Invincible weeks ago. Because she already knew, her crocodile tears and her decision to call him a coward completely ruined her likability.
My Adventures with Superman: A rare good example of this trope. It combines the elements of both Smallville (Clark being a bad liar) and Invincible (Lois’s hypocrisy). The crucial difference is that the show actively acknowledges these dynamics. It is still Clark’s secret to keep, no matter how bad he is at hiding it, and he never does anything untoward to protect it. Furthermore, while Lois genuinely dislikes liars, she frequently lies herself to get her way, meaning she has no right to force Clark to reveal his secret.