Warning: Spoilers below!
And oh, boy, this is where events spiral out of control.
Heres the thing: While Debs behavior is deplorable, Dan has this uncanny effect on people.

The CW
He crosses every moral boundary until the other person eventually snaps and wants him gone.
He cant put anyone elses needs before his own, as he adopts the my-way-or-the-highway approach to life.
Of course there will be fireworks at some point!

The CW
It isnt only a case of sibling rivalry; its a deep-rooted jealousy on Dans part.
Keith and Dans relationship hits its lowest point after Keith sleeps with Deb.
From there onward, it feels like all-out war.
Keith denies it, but Dan doesnt believe him.
Surprisingly, its the guilt from this event that forges Dan on his path to redemption inOne Tree Hill.
That said, the Dan Scott from earlier seasons… Sheesh!
Talk about the most reprehensible villain in teen drama.