Why did Yeung Teet Sum commit suicide?

[Ken Cheng]

Is there really any irony in the situation though?

Yeah...because of timing. Gwok Jing and Wong Yung first met Hung 7 Gung literally just a few days after Yeung Teet Sum's death, and it wasn't long before he befriended them, protecting them from the likes of Leung Tze Yung and Au Yeung Hak and teaching young GJ the Hong Lung 18 Palms. Imagine if that sequence of events had happened a week before YTS died. I could easily see H7G intervening, especially as he didn't have much love for the Jins and their minions himself. GJ and WY met H7G literally a few days too late to help YTS.