"Sentiment."
If he ever had to choose, Thor knew it would be him.
He was not his brother by blood; he was not his family by choice. It came down to family, and Thor knew everything he had ever told his team mates, his friends, every promise or statement or bitter words he ever spoke… they wouldn't stand up to the fact that Loki was his brother. Not by blood, but by bond, and that was enough for Thor.
All of his flaws, all of his mistakes and wrong steps and misdoings, all of it didn't compare. Loki was his brother; not by blood, but by bond, and that was good enough for Thor.
"Sentiment."
Maybe Loki didn't know it, maybe Loki didn't want to acknowledge it, but Thor hoped he knew all along he was good enough for his brother. The hurt and disgust and betrayal and hope and pain in his eyes, the misaimed stab, the purposefully misaimed stab and his knitted eyebrows…
Loki was his brother; not by blood, but by bond, and that was good enough for Thor. He has always been good enough for Thor. If he ever had to choose - the world, or him - he knew what he would pick.
"Sentiment."