About the book's first life.

1st Marriage

In the first life, Chen YanYun got married as per his parents arrangements. He didn't have deep feelings for his wife - Lady Jiang. They treated each other as 'guests'. He didn't sleep with her regularly, and so she gave him 3 concubines. He had one son by Lady Jiang, one son by a concubine, and a daughter by Lady Jiang in that order. He didn't really raise any of his children, leaving them to his parents to raise. He focused on raising through the ranks at work. He was a normal, poor husband I guess.

1st meeting with Gu JinChao

He visited the Ji family at some point and encountered a very spirited and bad tempered Gu JingChao. They did not meet face to face. He accidentally saw her, she fell into the water, he saved her. She never saw his face. He was a married man at the time and she was just a young girl, about 10 or younger maybe. He left the town quickly that very moment because he didn't want any ruined reputations.

1st wife's death

Later, Lady Jiang died and he used this excuse to 'practice Buddhism' and remain chaste from worldly desires for 2 years. He told his mother he wanted 2 years of mourning, for the only reason that she wouldn't urge him to remarry (as was the custom at the time). He literally had no interest in sex, women, alcohol, even his children. He was just a workaholic under pressure. After 2 years, he met Gu JingChao again by accident when her mother died and he was visiting her maternal grandparents' family. Note: she once again did not see his face or know who he was. This time he was not married and she was about 15. Something in his heart stirred but he went on his way.

His guilty deeds

He also was instrumental and complicit in wrongfully bringing down Changxing Hou and Ye Xian's family. Around that time, his faction implicated Gu JinChao's uncle and Chen YanYun and his mentor both wanted to kill all the officials and their families who they used in implicating Changxing Hou. ML literally had a list of officials and their family members whom he was marking for death/exile etc. He saw Gu JingChao's name and decided on a scheme to spare her family. ML was on the bad side in the first life.

2nd Marriage

At this time, everyone around him was urging him to get married. His mother was even at the point where she was like 'The next girl I choose, you will have to marry whether you want to or not." Chen YanYun thought of Gu JingChao and thought that if he was going to get married, it might as well be to someone he wanted to protect. So he, without her permission or even ever showing his face to her, proposed marriage to her family in exchange for not implicating them. Of course, they said yes. No one asked her. No one told her. Being a headstrong girl with lots of attitude, she of course did not want to get married to someone she didn't know.

Betrothal gifts

His betrothal gifts were 2000 teals and 10 gift boxes. At the time, the marriage was hasty, the bride had a bad reputation, and the ML and FL had never even met properly before. To FL, she had never seen or interacted with him at all before. This was still a proper, respectable betrothal gift, but nothing more. Contrast this with the second life where they interacted, knew each other, she consciously agreed to get married - His betrothal gifts were 4000 teals and 50 boxes of gifts plus various jewellery given from him and the Chen family at various times until she married into the family.

Misunderstandings and zero communication

When they got married, to him, it was a normal second marriage. To her, she was getting married to someone she didn't know in a muddle-headed kind of way. In the beginning they didn't know how to interact with each other because they didn't know each other at all. ML expected a normal, dutiful wife, but no one had ever taught Gu JinChao how to be a dutiful wife, nor was she the kind of temper to be a 'dutiful' wife without some coaxing. ML literally left her alone without even trying to speak to her, citing "she doesn't want to see me". He didn't bother to interact with her. In a strange place controlled by servants left by his late wife, 15 year old, headstrong Gu JinChao didn't really know what to do except pretend she had things under control.

To top it off, yes she liked Chen XuanQing and was jealous of the care he openly displayed to Yu WanXue. My take is that if ML had shown some of that care, Gu JinChao would realise that she was in love with the idea of someone loving her like that. She really just wanted someone to love her, and while ML protected her, he didn't show that he cared much (though he cared deeply). When he realised she might like Chen XuanQing, he didn't even ask her about it. He just left her to it. He failed to realise she was a 15 year old girl with 15 year old thoughts, and who was under pressure too.

(IMO, a 30 year old man with a full 10 years of marriage under his belt and grown children, had no business being peeved that his new and young wife had a crush on someone before him. He was an overthinking, introverted jerk who couldn't express his deep love to his new and young wife.)

The ending of the first life

5 years later, his faction killed him in a court scheme and his protection for her was gone. Chen XuanQing inherited, locked her in a side courtyard, took away her son and never let her see him. By this time she understood Chen XuanQing was not worthy of her love and was a beast in human clothing. She wasn't infatuated anymore. She didn't like or think about ML either. She eventually died and ...

SURPRISE! Chen XuanQing had liked her too, but despised himself for it. He turned his loathing onto her and treated her badly. I speculate he didn't love his wife as much as he showed he did. He treated Yu WanXue well only so Gu JinChao could see and be jealous. In reality, he was rather cold to Yu WanXue and took many concubines. In the end, even after Gu JinChao's death in the first life, he couldn't let her go, not releasing hr body to her servants for burial. In the first life and second life as well as the drama, Chen XuanQing was despicable.