In fanfiction, Oliver might use his skills and resources to help Barry heal from his hurt. This could involve getting him the best medical treatment or providing a safe place for him to recover. At the same time, Barry could rely on his speed to help Oliver in his fight against crime, which would show that their friendship is still strong despite the hurt. They could also team up to find out who or what caused Barry's hurt and take revenge together, which would bring them closer.
It's hard to say exactly without more context. Maybe he has a strong dislike for fanfic related to their world or characters. It could be that he feels fanfic distorts the 'true' story or characters in some way that he doesn't like.
In fanfiction, Barry's hurt could strain his friendship with Oliver in several ways. For example, if Barry is physically hurt, Oliver might feel guilty for not being able to protect him. Emotionally, if Barry is betrayed and hurt, he might pull away from Oliver, causing a rift. Their different approaches to dealing with problems could also come into play. Oliver might be more of a lone wolf and want to handle the situation on his own, while Barry might expect more support from his friend.
He might be frustrated with the way fanfic writers are using their characters. Maybe they're making the characters do things that are out of character.
One idea could be a story where Barry, Kara and Oliver team up to face a powerful new villain that none of them could defeat alone. They have to learn to combine their powers and skills in a unique way.
Barry Allen became The Flash after being struck by lightning while working in his lab. The lightning was charged with chemicals, which altered his body's chemistry and gave him super - speed. This event transformed him into the Scarlet Speedster we know as The Flash.
Overcoming personal challenges is also a frequent theme. Both Barry and Oliver have their own personal demons. In fanfics, they can support each other through these challenges. For instance, Barry might help Oliver deal with his past traumas, while Oliver could give Barry advice on how to handle the pressure of being a superhero in the public eye.
It's hard to say for sure if there is a great 'barry sings for oliver fanfic' without actually searching. But fanfic writers often come up with creative and unique ideas. Maybe there's one where Barry sings for Oliver in a really touching or humorous way. You should try searching on platforms where fans share their works to find out.