The survival of their friendship is uncertain. Oliver has a lot of pride and Barry is his friend. Finding out about the kiss could shatter Oliver's view of Barry. However, if they both value their friendship more than their feelings for Felicity, they could work through it. They might have to go through a period of awkwardness and rebuilding trust, but it's possible for their friendship to survive.
Well, Oliver might get really angry at Barry. He could see it as a betrayal since Felicity was someone he had feelings for. He might confront Barry and demand an explanation.
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.
Barry may face the challenge of controlling the baby's speed powers. Since the baby is a speedster, it might accidentally use its powers in a dangerous way, like running into walls or causing chaos in the city. Also, he has to figure out how to feed and take care of a super - powered infant, which is no easy feat as normal baby - care methods may not work.
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.
Maybe in the fanfiction, Flash discovers Peter's identity in a very unexpected way, such as seeing Peter's Spider - Man suit by accident. He then has to decide whether to keep the secret or not. He might struggle with his own jealousy towards Peter and the newfound knowledge. If he decides to keep it a secret, it could lead to an unlikely friendship between them, with Flash helping Peter in small ways without Peter knowing it's him.
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's relationship with his enemies could become more complicated. Some enemies might see the baby as a weakness and target it, while others might be intrigued by the idea of a baby speedster and try to manipulate the situation. This would put Barry in a difficult position, having to protect the baby while also dealing with his foes, and it would impact how he interacts with them.
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.