TLDR: It’s basically just years of misguided resentment and misunderstandings piled up and projected onto Yeonseo. Soohan’s personality has always been of the major and insufferable victim mentality kind.
1.) because his dad, despite being deadbeat and all Soohan had, nearly gave his life to save Yeonseo, 2.) because Yeonseo was born rich and privileged and Soohan wasn’t (inferiority complex), but Soohan thinks this automatically makes Yeonseo naive to the realities of the world and a snob 3.) because Soohan manifested as an omega, which felt like a death sentence to him (omegas have it harder etc), 4.) but Yeonseo manifested as an alpha, so Soohan thinks that means Yeonseo never has to work hard (because society favours alphas etc), 5.) because Yeonseo’s parents arranged them to marry which Soohan believed he was forced to do in order to secure his career/future (he’s kinda been sold off in his mind), 6.) he thought for looooooong time that Yeonseo was the one who S/A’ed him, that sustained distain isn’t smth that you can just shake off in a day after learning the truth.
He’s just always been so self absorbed and consumed by his victim complex, that he never bothered to look at Yeonseo properly

Help me understand why soohan hates yeonseo so much? Is it just because yeonseo is rich?