Well, it could be that Edward, perhaps jealous of Harry's popularity or a girl he likes, spreads false rumors about Harry. This causes Harry to be ostracized and his heart to break as he loses friends and respect.
In this fanfiction, it could be that Edward is in love with the same person as Harry. Edward decides to use underhanded tactics to win the person's heart. He starts by turning everyone against Harry, making Harry feel alone and unloved. This makes Harry's heart break as he not only loses the chance with the person he loves but also his friends and social standing.
Perhaps they are characters in a modern - day wizarding world where they are both part of a secret magic society. Edward could be a powerful wizard from an old family who feels threatened by Harry's new - found powers. So, he decides to break Harry's heart to assert his dominance.
Perhaps Tonks starts dating someone else, like Remus Lupin. Harry has some unspoken feelings for Tonks, and seeing her with Lupin makes him feel heartbroken. In the fanfiction, it could show Harry's internal struggle to accept the situation and his pain at seeing the woman he cares about with another man.
One possible plot could be that Snape reveals some long - held secret about Harry's parents in a very cruel way. For example, he might tell Harry that his father was not as heroic as he thought, and this shatters Harry's idealized view of his family, thus breaking his heart.
Well, it could be that Annabeth betrays Percy's trust. Maybe she lies to him about something really important, like her true feelings or her actions. This lie could be the start of breaking his heart.
Well, it could be that Artemis, in the fanfiction, has to make a choice that goes against Percy's feelings. Maybe she has some divine duty that forces her to break his heart. For example, she might have to sacrifice their relationship to protect her hunters or to maintain some sort of balance in the mythological world.
It could be that Sonic makes a comment about not believing in true love or commitment. Since Amy is so deeply in love with Sonic and dreams of a future with him, this comment would be like a dagger to her heart. She might then question her own feelings and the relationship she thought she had with Sonic, leading to a heart - breaking situation for her.
Well, it could be that Hinata starts to ignore Naruto for some reason, like she falls in love with someone else. Maybe she gets influenced by some external force or false information that makes her believe Naruto isn't good for her. This sudden change in her behavior towards Naruto would break his heart as he might have deep feelings for her.
Well, it could be that Hinata might break Naruto's heart by choosing someone else over him. Maybe she realizes she has feelings for another character, like Sasuke perhaps. This would be a huge shock to Naruto as he has always seen Hinata as a special person in his life.
Perhaps Ino lies to Naruto about something really important, like leading him on with false hopes of a relationship. She could make him think she has feelings for him, but then suddenly reveals it was all a joke or part of a mission. This would shatter Naruto's heart because he's so sincere in his emotions. He'd feel used and betrayed.
Another possible antagonist could be the Ministry of Magic. If they suspect Harry of something and force Tonks to spy on him or cut ties with him, it would break Harry's heart. The Ministry's strict rules and paranoia could be the driving force behind Tonks' actions that lead to Harry's heartbreak.