It could slow him down. Ash might be so distraught that he doesn't focus well on training his Pokemon. His usual enthusiasm for battles and catching new Pokemon might wane, as his mind is preoccupied with his broken heart.
It could be that there is some misunderstanding between them. Say, Misty misinterprets something Ash does as him not caring about her anymore. Ash, being clueless about her misinterpretation, doesn't correct it in time. Then Misty distances herself from him, and Ash is left heartbroken when he finally realizes what has happened.
Ash's journey also has its hardships. When he returns to Pokemon High School a bit down after a tough loss, Serena is there to comfort him. This shows that his journey, with all its ups and downs, gives them more opportunities to support each other and develop a deeper relationship. Their relationship evolves as Ash goes through different experiences on his journey.
Ash's Pokemon trades in a fanfic can greatly affect his journey. A new traded Pokemon might have different strengths and weaknesses compared to his previous team. This can force Ash to adapt his training methods and battle plans.
Ash's transformation into a Gardevoir would have a complex impact on his relationships. Some Pokemon that were once his rivals might see him in a new light and either be more respectful or more envious. His bond with his own Pokemon team would change too. They would have to adapt to his new abilities and appearance. And he would form new relationships with Pokemon that are more associated with Gardevoir's kind, like other Psychic or Fairy - type Pokemon.
The Pokemon that have been with Ash for a long time, like Snorlax, might have a deeper connection with him and be able to sense that it's still Ash, even though he looks like a hedgehog. Snorlax might be more accepting right away and try to protect Ash from any potential danger. On the other hand, the newer members of his team might be more likely to question whether this hedgehog - like Ash is still their rightful trainer. But as time passes, they would all start to realize that Ash's spirit and his bond with them haven't changed, despite his physical transformation.
Well, perhaps in the fanfiction, Ash is betrayed by a group of friends he trusted deeply. They might have used him to get access to some rare Pokémon or some important information, and then they turn their backs on him. This would be a huge heartbreak for Ash, who is always so loyal to his friends. Or it could be that he fails to achieve a major goal like winning a big Pokémon tournament due to some unfair circumstances, and he feels heartbroken as all his efforts seem to be in vain.
A new, powerful villain could be the cause. This villain might target Ash's Pokémon and manage to steal them all away. Ash would be heartbroken not only because he lost his Pokémon but also because he feels he has failed to protect them.
He might isolate himself at first. Natsu could withdraw from his friends and normal activities, needing time alone to process his pain. This is a common way for people, or in this case, characters, to deal with heartbreak.
In fanfiction, Ash might improve his pokemon's IV through special training regimens. For example, he could focus on specific battle scenarios that target areas related to IV stats like speed or strength. He might also seek out rare items in the fanfiction world that have the power to enhance these inherent values.
He could start with strict daily routines. For instance, waking up early for warm - up exercises, just like real - life athletes. In the fanfiction, this would show his dedication.