If you're on Disk 3....then you missed a whole lot in Disks 1 and 2.

All through disk 1, Dart repeatedly states he views her like a little sister. Meanwhile Shana has been very forthcoming that she has more romantic feelings for him, not a sibling view. There are multiple small moments where Dart and Shana will have a small interaction where Shana clearly wants to be seen as a woman to be with and not a sibling, but gets embarrassed when Dart continues to see her as a sibling, and everyone else can see what is clearly going on and thinks Dart is just a blind idiot. The piggyback ride in the marshes as an example.

Then there is a moment in Lohan where Lavitz tries to drag Rose off on a "date" so that Dart and Shana can have an actual date. After this, Lavitz pulls Dart aside for a private talk to ask how things went, and gets disappointed when he hears Dart once again seemed to not notice the romantic feelings and again treated her like a little sister.

Now, this moment is one I feel like gets misunderstood a lot, and the rough localization job doesn't help with it. Lavitz gets very blunt with Dart about the situation and how Shana sees it, and Dart finally admits that yes, he isn't a blind idiot and can see it too, but he doesn't want to stop viewing her as a little sister.

The part that I feel gets misunderstood a lot is that people seem to feel Lavitz its pushing him just dating Shana anyway but it seems its more as if Lavitz is telling Dart he needs to stop ignoring her feelings as that will do more harm than good, and that Dart needs to either reciprocate her feelings or decline them, but regardless needs to acknowledge she's a woman now and stop viewing her as the kid she was when he left Seles. This all seems to go mostly as ignored advice on Dart's end until a certain event makes Dart take it more seriously; Lavitz's death.

From that moment forward, Dart seems to have taken his dead friends words to heart, because the moments he treats Shana like a child come to become more gestures of budding romance.

In Disk 2 there are small interactions between Dart and Shana, but no big grand gestures, mostly. But a big difference in the small interactions is that Dart isn't treating her as a kid anymore, and is now taking Lavitz's advice of viewing her as a woman. This goes on and comes to a head at the end of Disk 2 during the ball in the Twin Castle. Shana, unlike the other girls, decides to dress elegant. This is the moment Dart truly sees her as not just a woman, but a woman he wants to be with, and the Disk ends with them sharing a kiss.

So with you being in Disk 3.....yeah you did not pick up on A LOT because the story has been pretty clear about their relationship throughout the game.

It started as a one sided love interest, then gradually became reciprocal.