I forgot the title..send help

so this is manhwa is about a girl who has a twin brother. However, her twin brother runaway together with his lover. During that time, the empire are under the order that all families should send their sons to the military training to subdue monsters who are threats to the empire's safety. So, she pretends to the her twin brother since they similar stature and she is more than capable at handling swords and have more combat capabilities. She is actually a daughter of the empire's greatest knight but her father fell into a coma state because of an illness. I forgot if she regressed or reincarnated but I remembered she knows the plot like who is the male lead and whatsoever but not in full details. So, she is serving the empire's prince - the white haired guy who has powers and is interested in her/him. Moreover, based on the novel that she had read in her pastlife, the male lead was the knight with brown hair (not sure about this) and that knight has royal blood so he is a candidate for the throne. She is in a love triangle or so they say. But, she is slowly realizing how absurd the novel was as the reality is quite different from it or was there an another season if the story she have read? But one thing is for sure, the male lead is a showing signs of a psychopathy or an obsessive characters, and true male lead might be the villain who was just misunderstood or trap by the empire's abominable orders.

ps: I just typed how I remembered the story and the flow.