I don't see how this is consideres out of character to people, the protagonist has always treated her situation with the belief that she knows what will and will not happen, one of them being the divorce. She's been preparing her whole life for what seemed like an inevitable future, do people really think she is suddenly going to think that its because the Prince loves her? The expedition arc showed this pretty clearly, the protagonist only sees the Prince as a dear friend, she was more surprised that the Prince had returned earlier rather than happy because her knowledge of the future was contradicted. On the Prince POV however, it is pretty clear from his inner monologues that he does love her, but this is never really shown very clearly to the protagonist. I don't think it's fair to say that the protagonist is dumb or not making sense, if anything, the problem lies in the dumbass cockblock fireworks as a plot device.