You might want to check out 'Secrets Unveiled'. In this story, Draco discovers Harry's abuse by accident when he follows him to an abandoned part of the school.
Well, 'The Truth Behind the Boy Who Lived' is a fanfic where Draco finds out. It happens when they're paired up for a project and Harry has a breakdown.
Draco's reaction could be complex. He has been brought up in a certain environment where showing weakness is not acceptable. But when he discovers Harry is abused, he may find it difficult to ignore. He might start by being a bit standoffish as he processes this new information. However, deep down, he might feel a growing empathy for Harry. His actions could range from small gestures of kindness, like leaving a potion that could help heal Harry's wounds secretly, to gradually becoming more open about his concern and trying to get Harry away from the source of abuse. This discovery could be a turning point in their relationship, leading to a deeper understanding and connection between them.
Harry's reaction would be complex. He has been at odds with Draco for so long that this revelation completely changes the dynamic. He would likely experience a sense of disbelief that such a thing could be happening to Draco. As he processes it, he would start to feel empathy towards Draco. Harry might approach Draco cautiously at first, not sure how Draco would respond to his newfound knowledge. But he would be determined to help in some way, whether it's by using his influence in the wizarding world or just being there for Draco as a friend. This could also lead to a significant shift in the relationship between the Gryffindors and Slytherins as a whole, as Harry's actions towards Draco could inspire others to look at Slytherins in a different way, seeing that they too can be victims of difficult situations.
In many fanfics, Draco's reaction turns into a sense of protectiveness. He feels a need to shield Harry from any further harm, whether it's from the people who abused him in the past or from the judgment of others. For example, in some stories, he'll stand up to those who make snide remarks about Harry's past, using his Slytherin cunning to put them in their place. He also tries to be a source of comfort for Harry, which is a big change from their initially antagonistic relationship.
Draco might initially be shocked. He could then feel a sense of protectiveness towards Harry. Maybe he starts to see Harry in a new light, not as his rival but as someone who needs help.
One popular fanfiction with this plot is 'The Unseen Bond'. In it, Draco's discovery of Harry's abuse leads to a complex relationship development. Another is 'Hidden Scars', where Draco becomes Harry's unexpected protector. There's also 'A New Alliance' which focuses on how the wizarding community reacts to Draco's new - found knowledge about Harry's situation.
Fanfiction.net could also be a place to search. However, the tagging system there might not be as refined as AO3. But if you patiently browse through the Harry Potter section and keep an eye out for the key elements of Blaise and Draco saving an abused Harry in the summaries or titles, you may come across some relevant stories.
One possible reason could be his family's status in the wizarding world. His family might be involved in some dark deeds, and Draco could be a target because of that. Another reason could be related to his own actions or attitudes that have made him enemies.
He may start to spy on Ron to gather more evidence of the abuse. Draco is cunning, and he would want to be sure of what he's dealing with. Then, depending on what he finds, he could either take matters into his own hands or inform the proper authorities at Hogwarts, like the teachers. He would want to be in control of the situation in some way.
Well, there are several fan fiction communities on social media platforms like Tumblr. You can search relevant tags such as #DracoHarry #AbuseDiscovery. There are often users who share links to interesting fan fictions they've come across. Also, some Harry Potter - focused fan fiction forums might have this type of story. You'll have to dig around a bit, but it's possible to find some real gems there.
One common theme is redemption. Draco's discovery can lead to his own redemption as he tries to make up for his past behavior towards Harry. Another is friendship. It shows how a difficult situation can bring two former enemies closer together.