
His memories will come back around the middle of his pregnancy and he will forget about what happened during his amnesia.
But it's so sweet nonetheless because amnesia!Soohan kept on telling Yeonsoo "trust me"/"trust my love for you" that when his amnesia was cured...he held on knowing that. And man...it made me love the post amnesia arc even more tbh

It's the cousin of Yeonsoo the one who appear in chapter 29 : Jo Juno.
Juno is also an alpha and because of his inferiority complex when he smelled Soohan pheromones back then he thought it was an opportunity to mess Soohan up because Soohan was in heat and an omega in heat generally in omegaverse can't defend themselves.

I reread your questions and I notice that I didn't answer all your questions in one go so sorry about that.
For you second question, Soohan would untangle everything when the story would almost reach its end. Juno frightened by Soohan who could denounces him for sa to the authority wanted to act first and make Soohan resigned/demoted by hurting his image but Soohan acted quickly and successful intervenes in Juno's scheme. In the final chapter of the main story (chapter 41) we can see his final ending.
For your third question, ironically the angst would began after the resolution of everything because the angst is mostly between Original Soohan and Yeonsoo.
I think the angst was not too long. There's a total of 41 chapters in the main story.
Chapter 34 begins the arc of the return of the original Soohan until chapter 41 which is the end of the main story.

If I remember correctly, in the novel it was never really clarified because Original Suhan only returns for eight chapters in the main storyline.
In the novel Amnesiac Suhan is blackmailed of his supposed infidelity in the end of chapter 28.
Following chapter 29, Suhan who can't remember the past, found out that the blurry photo of him with a man who is carrying Suhan at the entrance of an hotel was from 2 years ago thus before his marriage with Yeonseo. So Amnesiac Suhan concluded that whatever they have done in this hotel it would not be considered an affair because it happened before Yeonseo and Suhan marriage.

Firstly, Suhan never leave Yeonseo but intended to.
Original Suhan returns at chapter 34 in the novel in the middle/end of his pregnancy.
The main storyline have 41 chapters so we have 7 chapters of Original Suhan returns.
Because Original Suhan doesn't remember the period of time when he has amnesia, he felt like Yeonseo took advantage of his vulnerable state so Suhan (once again) couldn't forgive Yeonseo.
Suhan wanted to leave Yeonseo but him and Yeonseo made a contract for it because Suhan was pregnant and Suhan didn't want to raise the baby.
That's why they agreed that after his pregnancy Suhan would leave the baby to Yeonseo. He decided that after the pregnancy he would pack his bags and leave Yeonseo.
But in the end they make up so it's okay !
I think a lot of the readers and spoilers are missing a key point of the story. Before you pass judgment on how much you hate the MC or think he's a jerk for no reason you have to understand his character.
Well...imo from reading the novel, the story really is about Soohan learning how to love and let himself be loved. He didn't grow up experiencing love or accepting that his parents loved him. So with that in the way, it's easy for him to dismiss anyone's affection for just them wanting to serve themselves.
For example: ML's parents just helped him and his dad to save face, they gave him scholarship to promote their company, his own father just tries to be good to make himself feel better about being a thug, etc.
In many ways, Soohan is selfish and bitter who was hardened by a rough childhood under his absent father and abusive grandma. He had it so good under Yeonsoo's family but he's already put up a wall around his heart so he fails to recognize the good things. He had a father who is trying to make amends, a young puppy ML that loves him unconditionally, future in-laws that recognize his potential but his bitterness is stopping him from acknowledging all that. That's why I think the story is about Soohan learning to love and be loved.
He has a victim mindset that just grates my gears sometimes too. But that's just how he is. He's scared, he's insecure about his life, he has no real life purpose but to be successful and give the world a middle finger.
But I don't think I'd be any better if I were the MC.
Also, he has a real legit reason why he's cold to the ML before his amnesia.