What can he do?

Eddard stood there flabbergasted while Sansa timidly began to pick up pace. There was nothing he could do, Robert was the law in this land, fucking whoever he wanted.

"Your wife is unfaithful my liege, I caught her in the woods this night." Ned said, blushing angrily. "I know. I've been planning to do her in one of these days, I just wanted you at my back for protection." Robert replied, giving Sansa a quick spank.

"So these are your options. I would guess my wife has visited your chambers already, trying to convince you to side with her. If you take my guards and arrest her, while I finish with your Stark girl, I'll marry her on arrival to King's Landing, and Cersei is out of your life forever. You can even go back North if you want.

Or, you can stay here, I'll finish with Sansa and go back to my 'loving wife', we keep our alliance with the Lannisters and don't risk civil war, you also have your choice of strumpets over there. It's your choice." Robert spoke as he slid Sansa off his shaft, gathering cunny juices to spread on her backside. With a thrust, he insert himself into her tightest hole.