Okay what the hell happened I'm confused

I think the mother of the ML doesn't like the MC, so sent an Omega male to seduce the ML. The MC was visiting the ML at his office, with their child and caught what looked like the sent Omega kissing the ML.

The MC ran away in tears and the ML beat the living shizz out of the sent Omega and warned his mum to stop bullying the MC.

Okay but why did the seme look angry at the uke in the last chapter he even forced him