The words Loki spoke cut Thor more deeply than he was sure the other could've imagined. It pained him that he couldn't simply take everything back - he couldn't undo years of exile on a dead, hostile and uncaring planet, he couldn't undo whatever he'd done to even get them in such a state in the first place - he couldn't change anything, despite all the power he had and all of the things they'd both been through. Nothing could be changed. He couldn't imagine what the other had been through over the months, years, the day to day thoughts of exile and abandonment. Even though Thor had been living in luxury, he shared such a dilemma to a certain extent.
Not a day went by that his thoughts didn't linger on Loki. Before he slept, as he woke, his thoughts had been consumed by the guilt and the worry over the fallen prince - many would say he was only here to abate his own guilt, get rid of his own pained thoughts, and they would be more wrong than they ever imagined possible. The amount of love Thor still held for Loki surprised even himself, and he didn't want to dwell on such things. He was here to...help him, to attempt to even begin to scratch the surface of making up with the other.
"Loki, I came to...I don't know. In blunter terms, I came to bring you back, but I know that it is not so simple as just bringing you back. I don't know where to begin with explaining to you, Loki. There's nowhere I can start without sounding selfish, heartless, as though I am here for the good of myself and not for you. I wanted...to come to you sooner, but I was a fool. I was afraid that you would despise me and throw me out to my death, for this is all my own fault, the blame lying on myself," Thor stared over at him, unable to stop himself from trying to explain, trying to gravitate towards Loki again.
As Loki spoke, as his skin changed, Thor closed his eyes. The words pained him, and he hated to admit that because they weren't his words and he didn't deserve to feel like this for him. He was completely unworthy of Loki, and he knew it.
"It is nothing like that! I am here on my own terms, not as a king, but as Thor. Whether you like it or not, Loki, I'm here as your brother, and I'm here as somebody that cares for you," he sat down again, trying to warm himself on the pathetic fire he had managed to create, constantly fighting to stay alight against the winds filtering in through the cave. He fed it some more of the wood he'd found, wood that refused to catch fire at the best of times, making this planet all the more inhospitable.