>>12033616Watch the episode where Ash gets Charmander.
He still trusted Damien even after Ash tried to save him. He wasn't very gung-ho for his would-be trainer at first until the end. We saw Charmander was capable of both loyalty and defiance in the very episode he was introduced.
When he evolved, he tasted power -- not just the modest kind of power that a trainer could bring out creatively, the natural kind of power that made him crave strong opponents (Aerodactyl, Blaine's Magmar and that Poliwrath as examples) and not just the scrubs he felt he could easily beat.
While he never showed any signs of abandonment issues, he was in a situation where he needed his trainer more than he needed him. He got to see what it was like to be on the other side when he evolved.