Some guys cheat when they're drunk. Some cheat when they've had a finger of whiskey on the rocks which allows them to tell themselves they were drunk. Some cheat when they start feeling trapped, when they realize their life has slotted into an inescapable track once the mortgage contract was signed, or once the baby was born. Some cheat because they're scared their other half is cheating. There are as many reasons as condom flavors, really.
Tony cheats because he needs to get his mind off the fact he's about to die.
Does it even count as cheating, he wonders, while Nebula slowly rolls her hips on top of him. He's lightheaded from lack of oxygen and everything feels fuzzy, and he's also literally trapped, so a few of the other excuses might apply in this case.
His dumb dick stands hard and proud as the Stark tower. Tony almost wants to tell the little buddy to cool it, that such enthusiasm is useless now. It's not like there's time for Tony to sow his wild oats. Nebula rides him sinuously, her hands pressing down on Tony's chest. She looks wound tighter than ever but her movements are precise which is soothing. Her hands slide over the nanite depot above Tony's breastbone.
"If we survive," Nebula says before she has to stop for breath. "I’ll allow you to upgrade me with these."
"I am so honored by your trust," says Tony. Her metal parts move restlessly, whir and clank, and Tony is seduced into moving one of his idle hands to touch. The metal of her arm feels warm and slightly oily, and it purrs while Tony's palm slides up to her shoulder, then down to cup the side of her ribcage where metal ridges jut out like ribs.
"And then I will slaughter him," Nebula continues. Her voice is low and saturated with anticipation. "We’ll find him and I’ll slaughter him, and you can watch. He will be much weakened now, for years to come. I could kill him."
Tony wonders who is the realist here. Technically there's still chance for rescue. A miracle is a statistical possibility. At the same time he doubts it'll happen to them. Hope would hurt too much.
He realizes his hips have been hitching up for some time, and that surprises him. Nebula's warm, living cunt tightens around him in a way that all the same recalls the suction of a valve. She leans over him, too heavy, and Tony can feel the last of his nanites stirring out of their hold. Nebula makes a noise, stops moving and Tony comes. It's drawn out and sharp like asphyxiation orgasms often are. Nebula continues moving on top of Tony until his cock softens completely, then lies on her side next to him.
She stares at her own hand. "They covered me," she says, and it takes a second for Tony to realize she means the nanites.
He doesn't bother telling her they're harmless, that they probably just responded to some jumbled incoherent impulse from Tony's hindbrain. He doesn't try to pull up his pants either.
Which is why when rescue arrives in the form of Pepper in the deep-space-equipped suit he made her and which she refused to try on, Tony's rolling on the ground with his wet junk out and a metal tit pressed to his elbow.
It isn't quite the poetic reunion it should have been, what with Pepper coldly holding the oxygen mask to Tony's face because she’s professional like that.
The real trouble, like with any affair, comes later. After the Avengers - and guest stars - undo the snap and Nebula has her revenge. They hastily throw a big celebration, as you do when you manage to save half the Universe against all odds. It doubles as Tony's stag night because Pepper doesn't remember anything and the wedding is still tomorrow. The future bride's smile dims more and more the longer Tony avoids her, until he has to escape the room or blurt out something he shouldn’t.
He stands and breathes in the cool corridor outside the conference room that hosted the party, his drink on the ground by his foot. It’s so tempting to kick it and watch the pieces fly.
Unhurried steps echo behind him. He turns, expecting Pepper, but it’s Nebula. Tony knows she spend the evening glued to her sister's side, an easy to keep track of juxtaposition of green and blue moving about the room. He can’t imagine what she must be doing here.
"I need to show you something," she says. She offers him her hand, the mechanical one.
Tony takes it, turns it around. The plates and parts feel the same against his skin, the same as they did during their ill-advised fuck, his brain supplies helpfully. For a moment he feels like a passenger in his own body, a brain in a jar. Then the metal parts he's been caressing - examining, examining, Tony - seem to melt and crawl over his knuckles. His first instinct is to let go but Nebula grabs his wrist with the bare bones of her fingers. The metal wave ebbs and flows, almost friendly, almost caressing. His nanites trickle out of their container and down his arm as if to say hello.
"What the-" Tony whispers as the two streams combine. They pulse and bulge over Tony's hand, before suddenly separating. Tony's nanites spread sluggish tendrils up his arm but make no move to go back in storage even when he sends a mental command their way.
"They've been... feeding on me and multiplying," Nebula declares dispassionately. "On me and other things."
Her eyes lock on Tony's and Tony recalls Thanos's purple flesh, so many pieces it was hard to say if some were missing. Nebula was the one who pulled off the searing hot, noxious smoke producing gauntlet off Tony's arm and later everyone saw the corroded Infinity Stones looking like some potent acid had eaten away at them.
"Friday, run a full diagnostic," he orders. Friday's answer sounds in his head, no helmet needed anymore. Warning. Biomechanical mutations have been detected. Software incompatible with the primer has been detected. Reset commands have been denied. Warning.
The nanites were, of course, programmed to synthesize new tissue when Tony was hurt. Not simply connective tissue or Helen Cho’s artificial substitute that carried no genetic material but to replicate Tony’s cells.
Tony thinks about kids and how foolish he's been. He cajoled and coaxed Pepper into having children when he's already had two. Ultron, and then Vision, whose official papers even carry the last name Stark. And now, because Tony was on a roll, there is this thing. This rogue nanite colony that has cannibalized organic elements harvested from at least three species.
The thing keeps creeping up his arm, for all Tony knows eating his flesh before replacing it with itself. Tony's third born. The worst part is that he doesn’t feel alarmed and doesn’t know if it’s because the colony’s already affecting him.
There’s a shift in the mass of nanites, a happy ripple before it hugs even more of Tony. Tony feels a wave of protectiveness and hunger - for knowledge, to prove it’s strongest, best, most lovable - that reads very familiar and alien at the same time. They aren't his feelings but some of them might have been at some point, and now they're coming from the neural link between himself and the nanites that was supposed to only ever convey his commands.
Nebula takes a step closer to him until her whole body brushes his own.
"Thanks for the upgrades," she says, deadpan. Tony can't tell if she's sarcastic, and that's a first for him. She's half-machine, half-alien and near complete stranger. Or she was until Tony knocked her up or gave her the motherload of all STDs. Tony doubts he has anything in common with her now that their shared ambition to see Thanos' innards has been achieved. He shouldn’t trust her.
But she's also not Pepper. There are no hard truths Tony must reveal to her, no pieces of himself he must give up to make her happy, no responsibility to protect her. There's only this mystery organism they created and weeks of rubbing shoulders in their little walnut shell of a ship in which neither of them felt like the king of infinite space.
Pepper, Rhodey and the kid will be better off without him anyhow.
"I bet I can hotwire Quill's ship," he tells Nebula conspiratorially. "Know any decent watering holes in this galaxy?"
Nebula tilts her head, then takes a look over her shoulder at the closed door behind which her sister and her friends are still celebrating. "There are bounties on me on every inhabited planet I've visited," she says, and once again Tony can't tell if she's bragging or not.
"Then we'll go somewhere neither of us has been, Smurfette. Cover some new ground.
And they do.