My take on the catfish theory.
I firmly believe that Talia is a catfish and that Noel knew it almost immediately. let me paint the events on how it probably went down.
it begins with Misha meeting Talia online during the next couple days he begins "showing her off." Noel, being the only gay man in uranium, is well informed about catfishing pitfalls because of one bad experience and several hours of rabbitholing afterwards, and when he sees the photo his "spidey senses" are triggered. he then gets the idea that maybe if he proves talia is a catfish misha will start to like him(he knows of the chance it's not romantically, at first). so he begins to analyze the evidence he has gotten his hands on, and comes to the conclusion that talia is in fact a catfish. and the next day at lunch he has every intention of telling misha, but when lunch comes around he realizes "what if he hates me for telling him, what if he thinks I'm a stalker and creepy and publicly embarrasses me." he then runs to his isolation spot on the outside of then school building. and constance ,upon seeing him go to the spot and knowing what that means, decides to go over and ask what's wrong. noel then tells her everything because constance has that kind of sympathetic air that causes people to do this more than they care to admit. and when constance goes back in to sit with ocean, she(ocean) asks what that was about, and constance, without a hit of malice, accidently tells ocean after noel explicitly told her not to tell anyone. ocean ,shocked, drags constance over to noel with her and says to him "what!! how do you know? Are you certain? how certain are you?" noel then grunted and said to constance "I thought you weren't gonna tell her" to which she replied "sorry, it just slipped out" he responded back with," you're good" then shows Ocean his pile of evidence. she looks it over, looks at him, looks back at it, then looks at him with a determined expression and states no-one outside of this group will learn about this. and no one did until the events of the show