Well, in fanfiction, his classmates' reactions can vary widely. There are those who are his friends and they would be supportive. They might cover for him when he has to run off to be Spider - Man. On the other hand, there could be classmates who are envious. They might spread rumors about him or try to expose his secrets just out of spite or envy. And then there are the classmates who are just indifferent. They don't really care about Peter's secret life and just see him as an ordinary classmate most of the time.
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.
Deku's experiences with being bullied for not having a quirk. This would be important because it shaped Deku's character and his insecurities. Aizawa might focus on this to better understand the root of Deku's drive and his sometimes over - eager nature to prove himself. It also gives Aizawa more insight into why Deku is so desperate to be a hero despite the odds.
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.
Some classmates might be understanding. They could have been taught to be inclusive and kind, so they don't make a big fuss. However, there are also likely to be some classmates who are curious or even a bit mean. They might tease the child, not fully understanding the situation.