Maybe, while trying to protect her(maybe she was getting bullied? Other girls jealous or something?), he encountered “that” incident(s), which made him fear females!
Or maybe vice versa, she got hurt while protecting him from some girls at sometime, and he was scarred psychologically, that she was hurt because of him.
Something along those lines... I also think the “incident” might’ve something to with trains during rush hours, not sure though