It's been revealed to us, the readers, but no one in the story knows except Nea. As far as everyone else knows, Mana Walker was just one of the Noah (revealed to the Order's higher-ups via Cross, and probably the Noah through Wisely).
Controversial opinion, but it sorta seems like the FL was pretty toxic in the relationship as well? Their relationship lasted at least two years (before beginning of her second year to the beginning of her first year in university), but her internal dialog makes it sound like she never told him...