
Yeah... SPOILERRRRRR INCOMING
!!!! In the novel, it's revealed that Sangwoo was the result of an unplanned pregnancy. The parent who gave birth to Sangwoo was a male omega. The omega dad was in love with his alpha dad (the one who died in the accident), and thought that keeping the unplanned baby would tie the alpha to him. Turns out that did not work, and the omega dad ended up despising Sangwoo's existence so much he would beat him often and call him all sorts of names. So yea, both of Sangwoo's bio parents leave a lot to be desired.

Sorry but I'm only on ch 21. Literally just read about his omega dad today so it's fresh on my mind What I do know is that the blondie repeatedly rapes the MC, and when Sangwoo does find out, he doesn't go cray Cray as the MC would've expected. Instead he just laughed and let's it continue. But the stepson X stepdad is endgame (plus two twins) It's a 'happy' ending in that the MC builds a family with Sangwoo willingly.
Hmm looks like someone (his dad, or stepdad?) used to hit sang woo as a child