My head canon is this: The Discord of today is an adult draqonaquis. The didn't always look like that. Anyway, Tia always knew Luna felt under loved. But Discord and Tia were in love. Tia left Discord to take care of Luna, and it broke Discords heart. He became the god of chaos, forgetting he ever loved Celestia. Until season four, when Twilight returned his memory of how loyal Tia was to Luna, and he remembered, hence the flowers.