From what I understand, he interacted with the future her who came to the past and both of them grew close, but then she returned to the future (present?). The one in the past who was in control again didn't know him all that well and think they're strangers, but he wasn't aware of that. From his pov they're close enough for him to confess his feelings and she just suddenly distanced herself from him. And from her pov things are out of her controls but she was treating him appropriately given the circumstances.
Tldr; misunderstandings thanks to time travel shenanigans?