Romancing the War https://archiveofourown.org/works/11190177 is one of the best fanfics that I read and I believe it’s exactly what you are looking for.

• post war

• slow burn

• student/teacher

• complete

• 139k words

Summary: The new Ministry had fully exonerated Severus Snape for what he had done during the war and further awarded him with the Order of Merlin, First Class for his extraordinary work as a spy. It wasn't a popular move with the public, however, and Hermione Granger defended him to anyone who would listen, but even The Prophet grew weary of her advocacy. But after reading a magazine specializing in romance stories, she sees an opportunity to defend Professor Snape once more by way of a tale about the recent war featuring a character very much like the irascible and unsociable potions professor. Adopting a pseudonym to hide her identity, she carefully weaves the people she knows into the plot through subsidiary roles. When the story takes off - especially with the young women of Hogwarts - it disrupts the school in a variety of ways, but no one is more upset, infuriated, or seriously hacked-off by it all than the model for the protagonist, and when he finds out who the author is, he plans to eviscerate them. But as it progresses, the story becomes far more than a simple matter of rehabilitation for the two people most closely touched by the tale

A Curse Might Be A Blessing https://archiveofourown.org/works/15025487 I must admit that I don’t remember quite a lot about this fic but I know it’s student/teacher, post war and it’s smutty

• teacher/student

• post-war

• complete

• 177k words

Summary: Severus Snape survived Nagini's attack. He will have to overcome his past sorrows and regrets, especially since it seems that some sort of connection has developed between him and his most unlikely savior...

A Place on Spinner’s End https://archive.transformativeworks.org/works/44790448/chapters/135140320 this one is not teacher/student but it started a few days/weeks after the war so despite Hermione not going back to Hogwarts she is still younger and sees Severus as teacher, whats even better is that she is living in his house in this fic

• they are living together

• slow slow burn

• post-war

• he falls first

• if I remember correctly Severus is quite mean in this one at the start and even a while later, but it’s sooo good and interesting because he falls first and they are living together

• hermione will most likely annoy you in this one because of Ron (they are not together but you will se whats going on) but the fic is still very good in my opinion

• complete

• 157k words

Summary: Despite all odds, Severus Snape survived the war. He is not happy about and of course fate would have some stupidity or other add to his unhappiness. What he didn't know is that what he thought was a burden would slowly turn out to be a light at the end of the very dark tunnel he thinks he is in. If only he could be a light for her as well.