As others have pointed out, I think it is because she won and he did not. Granted that was his fault but when you have an ego the size of his, well sometimes you can't see the clouds from the trees (I totally did not mean to sound like Dr. Phil right there.). Also the core of that alliance was and always will be Fessy, Josh, and Kaycee. Amber, as she realized, is just a number to Fessy and Kaycee. I do think Josh actually likes Amber and wants to work with her and it is not just because of her being one of the best female athletes on the show.
Plus Fessy and Kaycee are probably always