Yes, Lauren betrayed her friend, but Brad and Brad alone made the decision to cheat on Terese and leave his marriage.
Terese certainly dominated Brad to a degree, but I didn't see him as being totally dependent on her. Brad isn't clingy and doesn't have low self esteem.
Also, I don't see Lauren as domineering or controlling. She making it clear she wants him, but he's making his own decisions.
There's absolutely no reason why Perdita should remove her post.