@Eeveechi I do believe the emperor JUST realized what happened.
He was always in love with the baron/count's daughter. He was pretty much in his rebellious phase. He wanted to marry her but couldn't marry his "innocent and pure " maiden. If I follow the whole story. The MC was the mature and responsible sibling in the duke/marquis's household. MC's younger sister "fell in love" with the emperor and decided to participate in the competition to select the next empress from the few selected candidates. The younger sister was a very passionate young woman. When she learned that the young emperor got a lover and was told by the emperor himself that he will never ever loves her, she exploded and fell in the traps of the emperor's mistress.
The younger's sister jealousy ended up dragging her entire family. MC's family died and then is reborn back to the time when her younger sister was going to participate in the empress competition. She decided to go instead of her sister. Since the MC is the more mature and "cold-hearted" sibling, she decided to sacrifice herself.
Move forward, the MC was told the same thing by the emperor. She knew what was going to happen so instead of crying [which she already did a lot in her previous life], she decided to place conditions to the emperor and arm herself with allies and what to do to prevent any sabotage made by the mistress. Now, we get to this VERY important diplomatic meeting between two strong empires. The dumb mistress was ready to "destroy the entire empire" by blaming all "incident" of preparing pork meat to gives to the wives of the emperor of the other empire. Things didn't end up as the mistress planned because the MC was ready to fight.
At night, when both parties, the emperor and empress, finished their diplomatic meeting, the emperor went to visit his beloved "innocent woman" [LOL stupid young man]. When he heard a woman's cry, he got worried. Then, he saw his lover crying and the slap marks on her "sweet" cheeks. He got mad and asked her if she was mistreated by the "evil" empress. The mistress said nothing. The emperor became mad and went out with his fork pitch ready to demand blood for the audacity of the empress to slap and hurt "his heart."
Of course, before he enters the empress's chamber, he overheard what actually happened with the mistress and what the empress did to prevent a possible war with the neighbor empire. He was very angry and still in doubt so he went inside and asked the empress if anything happened.
Since the empress said nothing of the incident and fight between both women, the emperor just went outside. Now the conversation he overheard is now repeating on his head like a broken disc. He can't believe that his mistress was planning to offend the women of the visiting emperor just to make his current empress look bad. He was fine with her fighting for his love with the empress but didn't expect her to go and do an insane plan that would involve a war between nations. He can't sleep and is in shock. He decided to go outside to dissipate his worries. Moments later he didn't expect to see the empress int he garden too and found her crying.
Of course, the empress denied. He was taken to the empress palace and her maid is trying to speak up for her. The maid is trying to defend the empress and is asking the emperor to rethink about the situation about the two women. According to what the emperor said, it looks like there is more going on between the count's daughter/ his mistress and him that he can't let go.