Here are spoilers from novel readers During the trip...ML straight up pounces on her many times while she feels guilty thinking about her friend. ML and childhood friend lied they were going out because they wanted to see if their love interests would get jealous. Childhood friend has a crush on another guy in the group (forgot his name) while ML has a crush on FL. Dumb plan cause none of that worked. FL ended up distancing herself more from ML cause she thought he was taken. Childhood friend trying to get with her crush wasn't successful either as she complained to ML about it when the trip was over. These two were running on one brain cell.
In the end, ML shows up on FL's campus. She was walking out of lecture with friends and ML gets jealous seeing one of her guy friends being close to her. They wonder who ML is and ML tells them he's her boyfriend much to everyone's shock. He drags her away. They end up doing it by the school. After doing it, he basically tells her she can't back out (from being with him). She asks what about their friend. Then, he eventually reveals the truth that he's not the boyfriend of the childhood friend and it was all a lie since the childhood friend was interested in the other guy. He also tells FL that she took his first so she should take responsibility. He kisses her and asks if she wants to continue in the car or stay there. That was pretty much it in the end.