I can undertand Tia much better now, if all the other routes harmed him and the country I'd have wanted to avoid it too, seeing how he treated the previous Tia, he treated her properly, he didn't show dislike, I guess it's normal that she won't have much faith that he really liked her, or that she could be a variable that can change this ending, I guess she thought it's much safer to go through the original plot with a known ending rather than improvise.