I think this deserves to be a slowburn. There's a lot of room for intimacy without attaching a label to it. A label that might make them feel awkward and uncomfortable until it's resolved one way or another. Although I do hope that we reach that moment here and that it gets resolved in the best way possible. Which is them having a hot book session in the library.
And while there's a lot to be said about how sweet and fluffy this is, I can't help but feel a bit anxious about how the story is going. This really is a bubble that could easily burst. All they have is a train ride home. This, of course, could be easily fixed if they just exchanged phone numbers (Unless they did but I really don't remember them doing so). Which isn't a bad thing.