ez1ollie said:
Have we seen them kiss before? I know that one time right before they got together, but was that the only kiss they've had?
We've seen them kiss 3 times. The first time was when Yamato forced a kiss by surprise. The second was during the training camp just before Christmas. The third time was when they visited a shrine during New Year Festival, although it wasn't explicitly shown. They probably kept on kissing more often after that third time; at least his action in this chapter implies it.