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In retrospect, Thor would have preferred his betrayal.
If Loki had been honest in swearing loyalty to Thanos, he would have become an enemy, but he would still be alive.
Instead, now Thor was alone, the last of the Asgardians, after the disintegration of their ship.
He had lost everything, once again.
Once too much.
Enough.
Waking up on the talking rabbit's ship was both a blessing and a curse for Thor.
He hadn’t reach the Valhalla, where Loki waited for him, but he still had a reason to be alive: tearing Thanos's heart from the chest with his bare hands, letting him experience the same pain Thor had felt in front of Loki's unmoving body.
He shifted on his feet, restless like a lion in a cage.
"He's in pain," Mantis murmured.
"Well, he has been floating in open space for who knows how much, I would like to see you in his place," Rocket replied.
"No,” Mantis shook her head and put her hands to her chest, “he is in pain inside: he is sorrowful, mourning,” a grimace of pain deformed for a moment her beautiful face, “and he is devoured by guilt."
"SHUT UP!" Thor yelled, and his voice echoed in the small cabin, making Mantis startle.
"Hey," Drax said, "calm down, you: I’m the only one who has the right to treat her badly."
Thor moved away from them, got close to one of the ship's portholes, and looked out: Loki's body was out there, floating in the sea of wreckage.
That same body that in the (few, too few) previous days he had learned to know, love and worship.
Along with that soul that he had never understood.
Thor had held Loki close to him in a last hug as the ship disintegrated around them, until he could, but eventually he had lost him.
"That man is dead inside," Mantis insisted, but Gamora stopped her, rolling her eyes.
"Yes, okay, got it. Enough is enough, Mantis: give him a break."
Thor leaned his head against the glass and closed his eyes.
That alien was spot on: he was torn by the pain of loss, but what really was tormenting him, was the guilt.
Because, when Loki had materialized the Tesseract, Thor was sure that he was about to betray him.
Yet another stab. Metaphorical this time, but not less painful. Only the umpteenth proof that Loki didn’t love him and that he worried only about himself.
This Thor had been thinking.
But Loki had shown much more wisdom than he did. He, who was only able to charge with his head, down like a bull in front of a red cloth.
His (beloved, lost) brother had simply played his few cards as best he could. Loki had been loyal to him, he had loved and protected him, so much that he tried that desperate and mad, mad, mad attempt.
By the time the elegant, sinuous dagger had materialized in Loki's hand, Thor had already foretold the end, an end he was forced to watch in silence, helpless.
While Loki was preparing to dart the dagger towards the titan's throat, Thor would have given his only eye and all the blood that ran through his veins, to be able to scream: "Don’t do it! It’s okay, Loki, I understood! Lower your head and live. You're all I have, don’t leave me."
But Loki had gone all the way, and now he was dead.
Oh, he had died with honor, and if Asgard had still existed, its entire population would have paid him the most solemn tribute.
Loki would have loved it.
But Thor didn’t care about the honor, the glory, or the pride anymore, because Loki was gone and he had brought Thor's soul with him.
Mantis was right about this, too: his heart was dried up, there was nothing but pain and regret in it.
And now, Thor just wanted to reach him, because he had loved Loki with all his heart, but he had never really understood him. After his own death, Thor had to find Loki, wherever his spirit was, hold him close, and ask him for forgiveness.
But first he had one last mission to accomplish.
Gamora approached Thor and gently touched him on the shoulder, handing him a bowl of hot soup.
"You have to recover quickly: we have a lot to talk about, and to do."
Reflected in her eyes, Thor saw his own determination to end Thanos's life.
He thanked her with a sharp nod, and focused on his goal: for Loki, to avenge him, to apologize for having doubted him.
Atonement.
After losing everything, there was nothing left for him.