One thing at a time...

A young fellow asks a girl, “Will you hang out with me?”

She laughs, “Are you mad? I am married?”

"I am aware of it and I also know that you are having an affair with your boss."

"Are you blackmailing me?"

"No, I just want to have some fun with you. What's the problem?"

"No, no, I can't."

"When you are already having an affair with one person, what's the harm in being with two?"

"I only cheat one person at a time."