Brainwashed
He's eating him away again, corrupting his head, unmaking all of him.
Loki thinks he's doing all of this because he wants to, because it is what survivors do, because his brother and others are simply doomed and this is the logical choice. Of course he has a million good reason to be doing this, of course it is the only possible course of action....
You do not want to do this.
He's making you.
Loki is just saving his skin like he's done so many times in the past. He has loyalty to no one, he's a god of mischief and will get in the good graces of whoever he needs to be on the winning side, get the upper hand, get as power and love of others as he can get.
And Thanos has simply too many people, and he did threaten him to torture him forever if he didn't hand over the Tesseract, there is nothing wrong with doing so, and allying himself with the man. This is how he has survived all that he has lived through, the Biforst, his attempted conquest, Svartlafheim, Hela. He's a survivor and he's doing only that, surviving.
You're his puppet.
Wake up and fight, Loki.
No, he cannot heed those voices, no matter if his gut tells him that they are right and that his whole internal speech is the one that is corrupted. But he cannot do anything, every time he thinks of moving away, of not doing what Thanos has ordered him... he simply can't. He has to.
Maybe is the power of the Tesseract who has messed up his head. There is a lot of power in that cube, and prolonged exposure surely caused problems. Not even Thanos himself handles them directly choosing to work them through a glove. So that voice is probably only that, a simple side effect of being around the Tesseract too much. He's doing the right choice.
You never had any options.
He always gave you the illusion of choosing.
He doesn't sleep anymore, and he has forgotten when was the last time he ate. He seems to have forgotten all the music and theatre he used to go back to in bleak times, and everything has been replaced with missions and strategies and plans to wipe out the Avengers. There's something wrong with that.
He got to your head.
There's almost nothing of you left in what you are doing.
You can tell just by looking at him that there's something wrong. He isn't simply sickly pale and bony, his skin is wrong, with uneven darker patches. He gets scratched and cut much more easily, and those injuries, however minor, never seem to heal. There's something external in him, that is interfering with all that he is, with his healing abilities, with his appetite, with the entirety of his being.
Why are you doing this?
He'll end up killing you anyways.
Loki is so incredibly tired, he's beyond exhausted and he doesn't have a moment to rest. Every little moment he's in tension, and he's constant fighting himself, as well as the others. He simply wants everything to end, for better or worse. There is a tear in his eye, as he unconsciously makes himself a very easy target for those Avengers. There is a shot and he's out.
When he wakes up, the voices are gone. The cube is too far and he is too far. But he is not yet free. Maybe he will never be free again. And all of this people, this whole world... They think him a mere lackey of Thanos'.
This was never what he wanted. This was the opposite of what he wanted.
His eyes are tearing up.
He is tied to some sort of metal chair, and the some members of the Avengers are in front of him, with angry expressions.
“Tell us everything that you know about Thanos' plans.”
“I can't.” Loki says, in a whisper.
I'll make sure you don't talk.
I'll make sure you can't ever betray me, little liesmith.
“Come again?”
There is an arrow between his eyes, but it doesn't change anything.
“Even if I wanted to, even if... I can't, I... he won't allow me. I really can't.”
And there's a feminine voice.
“He went in your head, didn't he?” It's Nebula. “Good. It's means he didn't trust you, which means you're not a brainless lackey.”
There's an intensity to her eyes that Loki likes. Maybe she can make the voices stop. Maybe she can fix him.
“Miss Maximoff can undo the... compulsion he's put on you. And then we can talk revenge... Revenge against him.”
Loki likes that.
He likes that very much.