So this is my theory:
Tidus will break up with Yuna, because he liked her shy personality. He will find out that he don't like new Yuna. He'll become.....but this is diffrent story. Let's back to the Yuna. Brother will start flirting with her and soon they gonna marriage. Yeah, that would be great! They are both so pathetic that they would make a perfect couple. And about Calli, I think she'll start dating with Clasco