I Don’t think he ever cleared that matter....
He probably got trust issues from being dragged in the war and got into thinking he would be burden on her if he gets close to her.....is what I think as per the stereotype male leads I know of (=・ω・=)
He only said 'the war broke my ability to feel emotion' something like that
I remember him having a flashback with the fl's mother I think so I thought that maybe something happened that made him misunderstand that the fl hated him amd that tje fl also thought that he stopped wanting to be friends with her
I'm sorry but I wasn't reading much of their dialogues but did Theo reveal why he was acting distant towards the fl when they met again? Cause I don't remember much of the bench conversation besides him confessing his love