We still don't know enough about the reasons she felt "betrayed" by Yai and Kaewta, but I think it's partly because she made up in her mind that she should be with Yai and that he must love him. Obviously, if he doesn't, it's because he was seduced and stolen.
I just can't believe she fell in love with her "foster brother". If we believe this conversation, they may not be blood related, but they were raised together. He sees her father as his own, so I think he also sees her as a sister.
Why would she think he would see her in a different way just because he offered her a nice hairpin? I guess the tragedy of what they had to live before could have been avoided if she just fell in love with another man. She is beautiful, so she could have anyone and probably someone who would really love her and only her.
