Wherever Peter is, he knows it's not Earth. In fact, he's not even sure if it's even in the same universe, the same reality as his home. For one thing, he no longer has a body. At least, not one he's aware off.
And that's another thing. Awareness is different here too. It's like he's a mind but one that can't do its job very well. It's as if he's permanently sleep deprived, so close to drifting off but with something there constantly keeping him perched delicately on the edge.
Peter's world right now isn't really a world. The best way he can put it is a vast sea of nothing. In theory, that shouldn't exist. Nothing can't have an appearance, or even a being, but there's no other word that fits. It's not dark, it's not light, it's not even something. He is just floating in absolutely nothing.
Sometimes, when the pull is stronger and his mind loses some of that fog, he can recall faded memories. He wouldn't say that's a benefit though because all he gets first are the memories of how he came to be there. He's burdened with the knowledge that he disappeared, that Thanos erased him and trillions of others from existence. He almost craves the nothingness then because anything is better than the reminder of how hopeless his situation is, of just how badly things have turned out. Not only has he essentially died but he's lost the peace he'd hoped the afterlife would bring him.
Mr Stark will save me
When Peter is at his most aware, he conjures the faces of his loved ones. He always thinks of May first. He remembers her smile, always there when he needed it and the smell of her perfume, a scent that lingered whenever she gave him one of her bear hugs. He thinks of Ned and how he's the brother Peter never had, the only person he could trust enough to be his guy in the chair. He imagines Ben, the only father he knew growing up and then, sometimes, he thinks of Mr. Stark. The man who'd been shaping Peter to be the best version he could be.
Though there's no way of communicating here, Peter knows he isn't alone. If he still had a body, he'd say it was like his spider sense. An awareness he wasn't alone but without the capability to see just who was there. He wonders if this place had been created just for them, the victims of Thanos' power, or if they share it with everything else which does not, or does not yet, exist.
If he could feel pain, trying to figure out how that worked would probably give him a headache.
The worst moments are when all Peter knows is fear and he can do nothing to fight it. He can't find May to give him a kiss on the forehead, Ned isn't there to distract him with jokes and there's no Mr. Stark to tell him that bad things happen sometimes but you have to stay strong.
Occasionally, the fear dissipates along with his consciousness and before he's lost again, he can remember that there are still people back on earth. Mr. Stark and maybe even some of the other Avengers. People who will still fight. He has to hope they do, that they're able to because even if he has no choice in the matter, Peter's not sure he can spend an eternity like this.
Maybe it already has been an eternity and Peter doesn't even know it.
No. Even if he doesn't technically exist right now, he's still an Avenger. Mr. Stark said so. Avengers don't give up, they don't lost hope. He can't lose hope. He still remembers the look in Mr. Stark's eyes as he vanished. He and whoever's left will save him, will save all of them. They have to.
…Right?