How is the relationship between the two main characters?

I don't have the hardware to play Tides of Destiny. However, I've read that the male and female lead during main story have a good chemistry. And can actually marry after. Though how is the relationship? Also, if you marry someone else, do the two stay close in any way? And can the two fuse again for say battle after being unfused (which is the premise of the game, where the two temporarily share one body)?