Ramble time (fucking shock I know)
So, Loki admits that he is jealous and planned on screwing up Thor’s big day, to get his brother to reveal his true colors. And the audience knows by the end of the movie that Loki does have power aspirations (which are exacerbated by having his fucking heart broken.)
HOWEVER
Look at the expression on his face as he talks about Thor. His face completely backs up the words he’s saying. the way he says “but” doesn’t apply the way it usually does.
It’s not “I love Thor more dearly than any of you, but *forget everything I just said*”
It’s more like “I love Thor more dearly than any of you, and because of this I feel I need to say this.”
There’s nothing insincere or ingenue about the first half of that sentence.
“I love Thor more dearly than any of you”
It’s true. He does love Thor the most, more than his parents do, more than their friends do, more than the people do, and because of this I think it does pain him to know that his brother (at the time) wasn’t fit for rule. Even though this fits well with his own power aspirations, it pains him to think of his brother as not being good enough.
After all, Loki knows more than anyone else what it’s like to not be good enough.