I don't know for sure. The ending of such a manga can be quite unpredictable and might not have been revealed yet. You could try discussing it with other fans to get their speculations.
I'm not really sure if they end up together. Different people might have different interpretations. Maybe you can dig deeper into the manga and form your own conclusion.
They could be in a situation where they have to work together on a project for the school. Karuizawa Kei is initially hesitant because she doesn't trust Ayanokoji. However, as they face difficulties during the project, Ayanokoji's calm and intelligent approach starts to win her over. Their relationship then blossoms from there. For example, they might have to deal with a tight deadline and scarce resources, which forces them to rely on each other's strengths. This shared experience can be the foundation for their growing relationship.
Reacting to Snape fanfiction depends on your own view of Snape. If you're a big Snape fan, you'll likely be excited to see different scenarios and stories about him. You could get really into the fanfiction that portrays him as a complex and misunderstood hero. However, if you have a more neutral or negative view of him, you might approach the fanfiction with more caution. Maybe you'll be more interested in ones that try to humanize him even if you don't fully like him.