Oh for god's sake, does it really have to be this predictable?
Irushia (dragon) somehow gains trust of human(s) (in this case, probably by saving the carriage) -> Irushia (dragon) learns that Irushia (hero) is a piece of shit -> Irushia (dragon) defeats Irushia (hero) and is cast out.
I didn't even have to wait to learn that the hero is rotten, because it was somehow obvious the moment they introduced him as a hero. Obviously, in a world where our MC is a monster, the hero has to be a complete, villainous PoS, right?