Hermione would be a likely candidate. She's always been there for Harry and is very empathetic. She would probably offer him some words of wisdom and a shoulder to cry on.
One reason could be that he's facing extreme pressure in potions class. Maybe he's constantly compared to others, like Snape always having high expectations of him. Another reason might be that he has some kind of emotional turmoil related to his past traumas while in the potions environment. For example, the smell of a certain potion might remind him of a difficult time at the Dursleys.
Severus Snape is another character who could be considered a potions genius in fanfic. In the official story, he was a master of potions. Fanfic writers might explore more of his early days as a potions prodigy or create scenarios where he imparts his deep knowledge of potions to other characters in unique ways.
Yes, there are quite a few. You can check out fanfiction websites like Archive of Our Own. Just search for 'Harry likes potions' and you'll find a variety of stories with different plotlines and writing styles.
Maybe he was poisoned. There could be someone who slipped a harmful potion ingredient into his cauldron without him noticing. It's a common plot device in fanfics to create drama.
It could be Malfoy. He often has a vendetta against Harry and might have found a way to make him collapse during potions class, either by tampering with his ingredients or distracting him in a way that leads to a mistake in the potion - making process.
In a more complex plot, Fleur could be falsely accused of a dark magic crime. Harry, knowing her innocence, tries to defend her but faces many obstacles. When he sees Fleur's spirit being broken by the false accusations, he can't hold back his tears. He might cry because he feels the injustice deeply and also because he's worried about what will happen to her.
Well, without actually reading it, it could be about Harry having some sort of emotional reaction related to Fleur. Maybe he's crying because of something she did, or something that happened to her. It could be in the context of their relationship in the Harry Potter universe, perhaps he has unrequited feelings for her or he's sad about a situation she's in.
I've read a really interesting 'harry cries hinny' fanfic where it was set during a time when Ginny was in danger. Harry's fear and his love for her made him break down and cry. It was really heart - wrenching. The author did a great job of portraying Harry's emotions, and how Ginny was his anchor even in the face of such distress. It showed a side of their relationship that was both tender and strong at the same time.