Some of these details may get tweaked as the game gets more complete, but for now, the basic explanation behind how Primrose starts to develop a crush on the player is that she doesn't really take him seriously until he demonstrates a clear interest in the things she cares about. She can appreciate being around him, receiving help, and even talking to him to a limited degree, but it's not until you show that you've read that book that she realizes that you actually care enough about her to spend time on something she has a passion for. She's a little slow on the uptake when it comes to anything social, so getting close to her is a little tricky. The idea is that she dislikes pushy people or people who insist on small talk for no apparent reason. What she wants is someone who respects her and can appreciate spending time with her sharing a good book, even if you don't talk.It isn't that you made her uncomfortable, it's that you failed to fully make her comfortable. If you want a more technical explanation, read the spoiler.
There are a few things you can do to test if Primrose has enough of a crush on the player to get that scene. If, when you first tell Primrose she's being investigated, she gives you a kiss, then you'll get the scene. If, after you work, you ask Primrose if she'll pay you with a kiss and she gets flustered, you'll get that scene. If you ask Primrose for her panties and she gives them to you, you'll get that scene.You don't have permission to view the spoiler content. Log in or register now.
In other words, she's a real introvert.