Alphard Grimm

I think it's different in the webtoon. I haven't read it but people say that he saw his dad cheating and dropped his phone so he wasn't able to answer Seyeon.

But he saw his dad cheating when he was young which was long ago.
Do you mean because he heard the manager talking about his dad's rumors, which made him frustrated so he couldn't pick up the phone?

Can anyone tell me why didn't Suho pick up the phone when Seyeon was calling him before he committed suicide?

Same. Didn't like the main leads & their age gap.