Married

Robert and Sarah weren't newlyweds, but they weren't an old married couple either. They had two children and a nice home.

Robert wanted more children, but Sarah wouldn't have it. He refused to get a vasectomy and wouldn't let her get her tubes tied. He still demanded sex, but Sarah was getting bored with it.

This left Sarah with one option in her mind.

Robert had to be prevented from impregnating her. And that would be achieved by making him a premature ejaculator.