This author really has good insight into the human heart. Baeksuns falling is accurate to how a super virgin like her would experience the process. Often, getting into a relationship for the first time increases pride, or at least forwards social confidence, one feels like they match adults around them more. For Baeksun this effect is much more pronounced due to being a shut in anxious introvert, so the ego boost from being chosen is increased further. Infact, she's so high on it, that she gloats to her cat.