Interruption.

(credit to user natalie16 for the suggestion)

Beth watched intently as Kyle's hand went up..and down...up and down. She couldn't resist. When he stopped stroking for a moment to rest his arm, she grabbed his cock and started jerking it.
"Beth!" it was an urgent whisper.
"It looked so nice..." she bit her lip. "I had to..." she stroked his cock, and with her other hand, she grabbed his, and began to pull it over into her crotch.

"Nothing's changed... just keep watching..." she cooed.
"This is bad..." Kyle whispered... but he started to finger her pussy anyway.
They masturbated each other as the porno flickered away, and it was lewd, and wrong... and very hot.
"You're good with your...f-fingers, baby." Beth spit on her hand, working his shaft harder and pinching her nipple until it turned purple.
"T-thanks...I guess.... you're not bad... with your hand..."
"I'm better with my mouth..."
"Fuckkk.... don't say things like that...." he was starting to sweat. His fingers worked faster, really digging into her snatch, and she worked his cock with a twisting motion that had him groaning softly.
"I'm going to cum..." he whispered, "...ssoon....if you don't stop..."
"Bet I can make you cum before you make me..." she whispered back. His fingers flew on her clit and into her pussy, and she began to squirm. "Fuck. Maybe...not...."
Just when Beth thought they might explode in mutual orgasm, a door shut upstairs.
"Shit...." Kyle fumbled for the remote, changing the channel away from the porno, while Beth grabbed a blanket and quickly threw it over their laps. She pulled her shirt down to cover her tits.
"Beth? Are you down there?"
"Yeah, baby. Couldn't sleep. We're watching TV." she tried to keep the tension out of her voice. Kyle had landed on an action movie. His face was bright red and his eyes were wide.
The stairs creaked as Brian came down the stairs, and Beth began praying internally. When he came into the living room, he was bleary-eyed and rubbing his face. He didn't seem to have his contacts in, and she thanked whatever god had listened to her prayers.
"Everything okay?" He rubbed her shoulder from behind as he passed the couch, heading to the kitchen. Her hand was still on Kyle's cock, and it squeezed involuntarily when Brian touched her. Kyle grunted.
"Yeah, it's fine. Just couldn't sleep, didn't want to wake you." She kept her sentences short.
"Oh that's okay baby. I'm just going to grab something to snack." He ambled over to the kitchen. "You want some beer nuts, Kyle?"
"No thanks, man. I'm... I'm good."
While Brian was looking in the fridge for a bottle of water, Beth began to slowly stroke Kyle under the blanket. He turned his face to her, full of panic, but she kept going, and soon, he was shaking his head in disbelief.
"fuck...." it was barely audible over the movie. Beth gave a wicked smile. This situation was so precarious...and yet... she couldn't help herself. After a few seconds, she felt Kyle's fingers on her pussy once again. It was so lewd, so brazen, that she had to fight not to cum immediately an give the game away.
Eventually, Brian grabbed a can of nuts and a water, and wandered back towards them. They both froze as he leaned over, and sleepily kissed her on top of her head. "Don't say up too late, okay?"
"Don't worry... I'm almost done." Kyle made a noise. "I mean... I'll be up soon."
"Ok..." Brian was, mercifully, too sleepy to figure out what was happening, and stumped back up the stairs.
"Jesus...." Kyle breathed. "I've done some fucked up stuff... but that might be....
"...the hottest thing I've ever done." She finished his sentence.
"Not what I was going to say."
"I don't care." Beth threw back the blanket. "Come here."

After all that jerking off, and the stealth act of infidelity, it took mere moments for Kyle to blast his cum into her mouth, which she slurped up before sitting back to swish around in her mouth and swallow while Kyle fingered her to an orgasm of her own.
"Jesus..." Kyle located his shorts, and was pulling them up. "Beth, we..."

Beth sighed. "I told you... we both needed to blow off some steam. It was fun." Beth almost expected her nose to start growing at how much bullshit she was spinning. "Now that we have, maybe we can both get to sleep."
"OK, I guess..." Kyle didn't seem so sure that their activities were perfectly okay, but he seemed to content to let it lie. "Goodnight, then?"
"Good night." Beth was seized by an impulse, leaping up to plant a kiss on his lips. "Thanks for sticking up for me." she whispered, before darting away to silently climb the stairs and swish with some mouthwash before getting back into bed.
You're insane!
It was fuuuunnn....
Were you trying to get caught?
No! Just... pushing the envelope.

She knew she couldn't lie to herself that well, but in any case, it was a one time thing. Wasn't it?
Sleep rolled over Beth.
Wasn't it?