But ever since the events of the first Thor movie, the two have taken drastically different courses in life, with Thor growing more humble and using his mighty abilities as a superhero, and Loki now more concerned with becoming more powerful, which he accomplished to a degree at the end of Thor: The Dark World when he tucked Odin away and disguised himself as the All-Father.
It’s only recently that Thor even learned about this deception, so it’s not surprising whatsoever that he’s is finally through with trying to find the good in Loki.
In the Marvel Cinematic Universe, Thor and Loki have both been around for over a millennia, and for most of their time together, they were the best of friends.