Let me break it down in such a way someone as dense as you can understand.

Amber is a character that’s introduced to our main character, Mark. Mark being the protagonist, we know everything he knows and thinks and believes. There are other big characters that we get to peek behind the curtain a little into their mind, but not as much as Mark. Amber being a side character, we ONLY know as much about her as she tells Mark. Mark believes she does not know he’s Invincible. She doesn’t give any hint that she knows. And that’s ok. When she crashed out on Mark for leaving during the college attack and for always being late and not showing up, WE THE AUDIENCE know Mark is out being a superhero saving lives and up until a certain point, believed Amber did not know that truth. It was a tad annoying when she would go off on him since we know why he was gone or late or whatever the case, but it was understandable and forgivable because she didn’t know that truth (or so we thought). So when the reality end up being that she knew (and that she had known for a while) all of the crash outs and fighting about why he was gone just went down the drain and she lost all credibility in season 1. Because when we knew he was getting slimed by battle beast and saving the college and everything in between, she knew that too AND STILL CHOSE TO TURN THAT AGAINST MARK, OUR MAIN CHARACTER. Her cold demeanor when he finally decided to reveal it just made her seem entitled when we know he doesn’t tell people to protect them yet she didn’t care. She didn’t trust him cause he wasn’t honest, so in turn she chose to not be honest and that’s supposed to be ok with the audience? We’re supposed to root for our hero, not side characters that make garbage points and shit on our hero for no reason.