There are multiple like that try being more specific.
I remember
I'm sorry i accidentally click post I remember the ml lent his jacket to the fl, then the fl has an older brother which accompanied her to the ml's unit to return his jacket.
That's all I could remember
Try this one "Hidden love: Can’
I’m not completely sure if it’s the one you are looking for but when I red your description it came to mind.
https://www.mangago.me/read-manga/hidden_love_can_t_be_concealed/
I remember reading a webtoon (?) Story about main leads who have mutual feelings but can't confess