There are fanfics where the 'lov capture deku' scenario leads to an exploration of Deku's character growth. For example, while captured, he might start to understand the motives of the LOV members on a deeper level, which in turn changes his approach to heroism in the story. This can add a lot of depth to his character.
You can start by searching on popular fanfic websites like Archive of Our Own. Just type in 'lov capture deku fanfic' in the search bar and it will show you relevant stories.
Deku might be completely shocked at first. Since Bakugou has always been so aggressive towards him, he would never expect such a confession. He might just stand there, mouth agape, not knowing what to say.
He might cry a lot. Deku is very emotional, and being cheated on would be a very painful experience for him. He could also get angry, which is rare for him, but this situation would be so unjust that he might not be able to hold it in. He'd probably start to question his self - worth too, thinking that there was something wrong with him that made his partner cheat.
Deku might be initially shocked. He's used to Bakugou's aggression, but an actual injury is different. He could be in pain and disbelief at first. Then, he might try to downplay it, especially if he doesn't want to cause trouble for Bakugou, because Deku is generally a very forgiving character.
Well, some might be really amazed. They could see a new side of Deku that they never knew before. His singing might show a different level of confidence or a hidden talent, so they would probably cheer him on.
Some characters might try to understand Deku's motives. Kirishima, who was close to Bakugou, would be angry at first but might also try to find out if there were any extenuating circumstances. However, many would be afraid of Deku, seeing him as a threat now that he has killed one of their own.
Uraraka would be heartbroken. She was one of Deku's closest friends. She might lose some of her usual cheerfulness and become more focused on finding out who or what was responsible for his death. She could also struggle with her own self - confidence in using her quirk, as Deku was always an inspiration to her.
One popular 'dark deku fanfiction' might be those where Deku turns against the hero society due to being constantly underestimated. In these stories, he could use his intelligence in a more devious way, perhaps forming his own group to challenge the established order.
One common theme is probably the 'opposites attract' scenario. For example, a very bubbly and outgoing character falling for the more reserved Suga. Another theme could be 'finding love in unexpected places', like on a tour or during a random encounter.