FL Clearly Falls First

Years before

Years before

Years before... sort of (it's complicated)

Years before

Years before

A love potion causes the FL to falsely think that she's in love with the ML early on. After the affects of the love potion are cleared, she falls for the ML for real. The FL is definitely the first to truly recognize her feelings and to confess. The timeline for exactly when the ML falls for the FL is quite unclear, but her confession forces him to evaluate his feelings which he sort of seems to recognize shortly thereafter.

The ML finds the FL interesting from the moment he first sees her, but he is still hung up on the SFL at that point. The FL is the first to develop romantic feelings.