I think he was also forced into a political marriage and to him his partner looked like he was out to get whatever he can from him. Which is kind of true bc the adoptive father really only adopted the guy so he can use him like that. I think the suic*de was like a slap in his face to make him realize that he was not the only one bound in a loveless marriage against his will. And he treated MC worse than any normal partner could. He probably never thought of that probability before bc MC had a lot to gain from ML. It was truly an unqual marriage like the ML said in one of the chapters. Also, the recent chap makes it seem like he really doesn't like his own family. Especially with him probably getting sidelined in succession despite his achivements bc he was simply born later.
Oh so it was like that , this contractual marriage was truly a black mark in both of their lives.
Where was this level headed Alpha in past Life ? Only if ....