Hides the secret phone in the first aid kit and waits

Hiding the phone in the first aid kit is easy enough - it has all sorts of compartments and Cynthia easily finds one which leaves only a minimal chance of the phone being accidentally discovered. Then begins the waiting game - turning off Mark's ability to get hard, have an orgasm or ejaculate whenever Cynthia's not around. She comes to call these three settings his "cockblocks" when she thinks about them. She turns them off when she goes to sleep, too, so that she knows he's not sneaking off to masturbate while she's asleep. It's ****, not knowing whether Mark has tried to cheat on her again yet. She desperately wants to be there to see his embarrassment and Vanessa's disappointed face as he explains that he just can't seem to get it up. Ugh, Vanessa. Cynthia's still not sure how to deal with that problem. She wishes there was an iCunt app which would allow Cynthia to close up that bitch's hole, but alas. Instead, she'll just have to play along like everything's fine while she waits for the answer to come to her.

Another difficult thing is resisting the urge to fuck with Mark's cock more conspicuously. In order to make sure everything seems like business as usual, she knows that her and Mark can't suddenly be having sex every night, and that she can't go straight to making him jizz in his pants the moment he sees her (although that wasn't off the table, further down the line). Instead, for the first few days, she raises his arousal only a little when she gets home from work and before he wakes up in the morning, and by the third day after that first night in the kitchen, there's a definite air of unease and pent-up sexual energy about Mark.

"Are you okay?" she asks as they sit on the couch together after dinner (and after her discreetly turning off his cockblocks and raising his arousal a bit for good measure).
"Yeah, I'm fine," he sighs, "I just... had a work meeting today which didn't go as planned."
"That sucks," she says, leaning her head on his shoulder, "Wanna talk about it?"
"No," he answers, a little too quickly. He turns to kiss her and puts his hand on her thigh.
"Do you want to?" he asks.
"Sure!" she says, smiling with the knowledge that his sexual stamina is turned down just as low as it was last time.

His cock is already hard, and she rubs it through his pants as the two of them make out as they reposition themselves on the couch. He jerks his hips away as she squeezes his shaft through his sweatpants, and she realizes that even that stimulation must have gotten his sensitive, **** cock close. She whips off her shirt and wriggles out of her pants and panties. She unhooks her bra and tosses it away. He takes off his shirt and pulls down his sweats, letting his hard cock spring free. Cynthia reaches out and strokes it, noticing with delight the excessive amount of precum it's already drooling out. She runs her hand up and down it's length before he snatches her hand away and pushes into her. The moment the head of his penis slips inside her, it begins to spit hot cum.
"Ooooooh fuck," he grunts as he buries his throbbing cock in her pussy.
"Whoa! Again?" Cynthia exclaims. Mark's too busy cumming to reply. He stays buried deep inside her as, panting, he comes down from his orgasm.
"Sorry," he says eventually.
"What the hell was that?" she asks in an astonished tone.
"I don't know," he answers, clearly ashamed. He pulls his softening cock out of her and she lies back for a moment before heading to the bathroom to masturbate and to put his cockblocks back on.

For the rest of the week, Cynthia repeats the process of cockblocking him whenever he leaves her sight and raising his arousal when she's around her. On Friday night, Mark attempts again to have sex with her. This time he takes slow, deep breaths and fucks her at a cautious pace and manages to last almost a minute before prematurely ejaculating once again.
"That was much longer than last time!" Cynthia remarks afterwards. She has a feeling it makes him feel even more insecure about it when she tries to reassure him. He doesn't say anything until after she emerges from the shower.
"What are we bringing to Darren and Jade's pool party on Sunday?" he asks. Oh shit, with everything else going on, she'd totally forgotten that Monday was a public holiday and that their friends Darren and Jade were taking advantage by hosting a pool party at their house.
"I totally forgot," Cynthia admits, "I guess I'll make Caprese salad. It always gets eaten, and nobody else will be bringing it."

But crowd-pleasing appetizers are hardly Cynthia's top priority, because Vanessa will without a doubt be at that party.