When Ah Zhi was saved from brothel and fl+family/companions gave her travelling money to return home. I was confused bc didn't her family sold her to the brothel, so by returning her doesn't that give them another chance to sell her off again. Heh I was right. I guess this had to happen in order to find Jier's whereabouts. This drama has karma elements. If fl didn't take AhZhi in, as a homeless person, then they wouldn't have found out Ah Jier's location. if they weren't kind to AhZhi she wouldn't have inform fl of Jier. Good karma comes back to you.
He always offers them great advice too! He takes their problems seriously, is willing to build them up. For Xiuwan,…
He's honestly not a bad person. i think, bc he's always born with a silver spoon, so he typically gets what he wants (excluding work and politics here). So he overlooked fl's feelings bc she was born lowly, and who wouldn't want to marry all the way to the top as the madam. So I kind of get why he slipped.
We can all yell and criticize ml, but he is an awesome brother. Typical men during that period, idk if Ming era is more open minded, would hole women in their household and never let them out in fear of ruined reputation and keeping them pure. But, ml is willing to take his sis to capital in hopes she broaden her horizons.
Are you actually watching? She slapped him bc he disrespected her and her family. Even commoners would have a matchmaker come to the female's house to ask her parents for hand in marriage. He didn't give her any courtesy and just had a stranger force her hand in marriage by a royal decree that no one can say no to. He didn't confess or give any hint to her.
During the scene where he was trying to persuade her to move to capital, and then mentioned Han scholar going to the capital for an exam, she had every right to throw a fit. He was ruining her reputation. No matter how much she hate this marriage and him, she is now married to him. That's a fact. By him saying this and presuming her of this, it's slander to her name. Reputation is still everything during that period
"First there was a departure without so much as a word, an then a marriage without even a whisper-always guided by the Lin family's interests and LJQ's own wishes, with no regard whatsoever for LX's feelings. That slap at the wedding was LX's reward for LJQ"-agree
That wedding pastry with "Lin" stamped on it is such a mockery for fl. Her crying while forcing herself to swallow that pastry was such a heartbreaking action. It meant she accepted fate.
The significance of Mr. Lu bringing out the royal decree and having fl's adopted dad mention the royal decree out loud when ml was picking up his bride. Such a smart move. This is to prevent any awkwardness and others looking/disapproving of the wedding (at least not openly).
K-Drama 
During the scene where he was trying to persuade her to move to capital, and then mentioned Han scholar going to the capital for an exam, she had every right to throw a fit. He was ruining her reputation. No matter how much she hate this marriage and him, she is now married to him. That's a fact. By him saying this and presuming her of this, it's slander to her name. Reputation is still everything during that period