First of all Sasuke isn't soloing Sakura in bed, He can't even escape her clutches.
Secondly. Sakura doesn't get knocked up, she harbors life in her holy body, nurtures it, and gives birth to a beatiful evolved being, like no other.
ANd believe me Sasuke didn't leave Sakura by choice, he left because there was no other option. Sakura is like a drug to him, She is too addictive to get over.