The truth.

"So, yes, to answer your question, I am married." Bella's face tightens a little, and she draws her hand back. "And Jenna, my wife is back at the club."
"Ok..." she sounds....disappointed? She chews her underlip, before giving a sigh. "That's a shame."
"...it doesn't have to be." You say, and Bella gives you a look of disgust until you put your hands up.
"No.,.. it's not like that. Jenna and I.... well...." you swallow. "We have an arrangement." Bella looks dubious. "We have... an open marriage. She's probably indulging herself right now."
"Wow... I guess I just thought that wasn't a real thing. Just something you read about in Penthouse or shitty erotica."
cough cough
"Yeah it's... different. We're still pretty new to it." You smile. "So...cards on the table... I know we just met, but I think you're gorgeous."
Bella blushes. "Thanks." You reach out to take her hand, hoping that she'll respond favorably.
She looks down for a second, before lacing her fingers together with yours.
"I bet Bradley would be super pissed if he could see us right now." she's staring into your eyes.
"He doesn't deserve a girl like you." You lay it on thick, and by her blushing smile, she's taking the bait.
"Stop..."
"I can think of a few other things that would piss him off even more..." you lean closer, and Bella bites her lip.
"Oh, can you now? Well..." she leans across the table to whisper in your ear. "My apartment is a ten minute drive away. Why don't you show me what you're talking about?" Her moist, hot breath tickles your skin as she trails her mouth along your cheek, and you seize the initiative, kissing her pretty plump lips. She hums and reciprocates, snaking her tongue in to mingle with yours.
"You're a good kisser, James."
"Let's get out of here, and I'll show you what else I'm good at."
Bella laughs.