Invite Dan and Gina over. Without any pretense.

"Oh, yea, we can do that. So long as I get to fuck Gina again, I'll let you fuck Dan again while I watch.
"Cool, thanks honey," Melanie replied. "I know you'll love it."
"I'm not sure about that. Letting you do it was one thing, seeing it though... I dunno."
"Well, I'm doing it again anyway, but I'd love it if you watched. So shall we invite them both over for dinner?"
"We could do, but why bother. Apart from Dan, we all know what's gone on."
"Oh, so...." my wife began, before trailing off.
"Well, I thought I'd just ask them both to come over for sex. I'm sure Dan will jump at the chance to fuck you again."
"Maybe," Melanie said laughing, but I don't know. He was keen today, yea, but we were alone. He might not want to come over here and do it with you around. Not without **** at least."
"Hmm, we'll see how it goes. For now, lets watch the last of that show you love so much, and then head off to bed early."
"Early? Why?"
"Well, we're going to need to get sleep when we can I think, if were going to to be having as much sex as it seems like we'll be having in future!"
"Yea, okay. You're right, Alex. Just make sure you ask them tomorrow okay?"
"Will do."

We snuggled on the sofa, and had a good night's sleep... after a longer than expected session with our heads between each others legs.

The next day after work just as everyone else was heading out, I asked Gina to come with me and went into Dan's office.
"Oh, hi Alex, Gina," he mumbled as he looked up, still seeming a little asleep despite the coffee Gina had made everyone, that he'd drunk most of throughout the day.
"Well," I began, glancing back at Gina, "Someone told me that you were a little... occupied last night."
Dan suddenly looked a little more alert. "Occupied? How so?"
"Well, I'm told that my wife was here last night."
"Oh, yea, she just popped in to see if you were here, but I told her you'd gone home."
"Yea, I heard that. But I heard a little more too."
Gina's head was swivelling back and forth like someone watching a tennis match. I'd not told her that Melanie had had sex with Dan, but by the look on her face I guess she'd figured it out.
"Uhh... yea... we talked for a little while..." Dan tried, before I went in 'for the kill'.
"I heard you had sex with her."
"What No! No I didn't. Who lied to you like that?" Interesting, he'd gone from denial to being on the offensive in a couple of seconds.
"She did."
"Gina?"
"No," I said before I got Gina in trouble. "Melanie did."
"What?"
"Yea, I knew about it. I said she could actually."
"What? Really?" Now he seemed to be in denial again.
"Yea, and the thing is, she wants to fuck you again."
He looked smug. "Of course she does. I know how to please a woman."
"Yea, anyway, we want both of you to come over tonight... For a little private party," I said, diplomatically avoiding telling Dan that both Gina and Melanie had said he didn't know anything about pleasing a woman, but that the power of his tool made up for his complete lack of skill. I might be paraphrasing slightly. Sue me.
"I'll be there," Gina said, speaking for the first time since we'd entered the office.
"What about you?" I asked Dan.
"Well... Okay. I'll call my wife and tell her I have to go out with some clients or something. This isn't some kind of trick though right?"
"Of course it's not."
"And I get to fuck both Melanie and Gina?"
"Yea, and probably get to watch them too."
"No way, are you serious?"
Gina blushed, but replied for me, "He is. We did it a few nights ago, and I'd love to again."
"Shit."
"You want to fuck Melanie as I lick her and you, Dan? We can make that happen."
"Damn, Gina, I didn't know you were into girls too. Fuck. You know what, I think we've done enough work for the day. Come on, we're heading over to your place now."
"You're the boss..." I laughed as we left.