
It's totally revenge. He marked an Omega when he was in rut. He thought the guy he was sleeping with was a beta.
He feels lied to, taken advantage of, and to top it all off he has a kid he never got to meet who looks just like him. And his kid is sick and didn't need to be. So, he's going to torture his partner for about 50 chapters, rape him often, and possibly knock him up a second time, all the while letting him know just how helpless he will always be. And y'know what, I don't blame the omega for never approaching the guy. He's an ass.
There's no love here. There never was. Just revenge and a need to control. Oh, and he gets to dangle his newfound wife as bait in a familial power struggle he won't understand for about 45 chapters. These 'plots' all go the same way.

His kid is sick but didn't need to be?!? He is such because he had inherited that gene. Unless you mean Noah didn't seek him out to get better treatment for their kid, then yeah, he's not being well-treated so he's constantly drained and sleeping. I'm not sure it's revenge. He is definitely using them. Can't claim absolutely zero sense of love until we see more. But anyways, there is no need for love to raise a child together. But their relationship is coercive though. That I agree.
I dont wanna be saying hate against Do yoon yet until I know what happened to him during the timeskip and what his real intentions with Yejun are. I dont think he just wanted Yejun to just suffer. He looked like he is obsessed to him now like he doesnt want him to run away again that's why he wanted to marry him asap