After Snape discovers the abuse, the relationship undergoes a major transformation. Snape begins to protect Harry from not only the Dursleys but also from any potential threats at Hogwarts. Harry, who has been starved for positive adult attention, starts to trust Snape. Snape, in his own brooding and complex way, starts to care for Harry's well - being. He might even start to teach Harry some advanced magic that he wouldn't have taught him before, seeing Harry's need for strength and self - defense in the context of his abusive home life. This new relationship dynamic is a far cry from their initial animosity.
Harry might start to receive more protection at Hogwarts. Snape could put in place some measures to keep him safe from further harm. For example, he might assign some students to keep an eye on Harry when he's in vulnerable situations.
Snape's reaction could be quite mixed. On one hand, he might be angry at Dumbledore for not doing more if he knew about the abuse. He may also feel a strange sort of empathy towards Harry. After all, Snape himself had a difficult childhood. So, he could start to be a bit more lenient with Harry in his classes and try to subtly offer support.
The relationship becomes more protective. The Weasleys will be more cautious about Harry's well - being.
In the fanfic, Snape's reaction could be multi - faceted. He might start by investigating the abuse more deeply. He could use his skills as a Potions master and a former Death Eater to find out who is behind the abuse. And then, he might take steps to ensure Harry's safety. This could involve enlisting the help of other teachers or even trying to get Dumbledore more involved. He may also start to teach Harry some extra skills or give him potions to help him deal with the emotional and physical trauma of the abuse.
Snape's reaction could be multi - faceted. He might be angry at those who are abusing Draco, but also a bit conflicted because of Draco's family's ties to the Dark side. He could use his position as a teacher to give Draco some extra guidance and support, perhaps in the form of private tutoring sessions where he can also check on Draco's well - being more closely. He may also start to question his own views on the Malfoy family in general.
Harry's life would likely become more stable. He might get proper care and attention, which could improve his academic performance at Hogwarts. Also, he could start to make more friends as he is no longer burdened by the secrecy and pain of the abuse. Dumbledore might arrange for him to have some kind of therapy within the wizarding world to deal with the emotional scars.
The impact would be significant. Harry has always had a complicated relationship with Snape. When Snape discovers Harry is gay, it could shatter some of the pre - existing barriers between them. Snape, who has his own secrets and pain, might find a new connection with Harry. This could lead to a transformation in their relationship. Harry may start to trust Snape more, and Snape could finally let go of some of his old grudges against Harry. They could end up having a more positive and supportive relationship, which would be a huge change from their often - hostile past interactions.
Their friendship would become deeper. Ron would be more protective and more attuned to Harry's emotions. There would be a new level of trust as Harry has shared such a difficult and personal experience with Ron.
In such a fanfic, Snape might initially be shocked. Given his complex relationship with Harry in the original series, he could struggle between his old grudges and his sense of duty. He might take it upon himself to protect Harry secretly at first, perhaps by using his position at Hogwarts to keep an eye on Harry's abusers. For example, if it's the Dursleys abusing Harry, Snape could find ways to make sure they don't go too far without revealing his true intentions.
One place to look could be Archive of Our Own (AO3). It has a vast collection of fanfics, and you can search for ones with this specific plot. Just use the search bar and type in relevant keywords like 'Snape finds abused Harry'. Another option is Fanfiction.net, though the tagging system there might require a bit more digging to find exactly what you want.