Not a secret

Wherein the people around the couple know they're together

Best friend and rivals know, and they kiss in front of the entire school, lol, so yeah. Def not a secret

Literally anyone who sees them together is able to put the story together, they're so infatuated with one another, it's sweet

Certain people around them know, notably rivals

Yeah, everyone knows everything around here....

Rivals, teachers and Tomoe (my beloved) know

Coworker knows

They're engaged, so family and coworkers are all aware of the relationship

Brother and students know