Seto has to be pushed and cornered for him to take action, but when those dire times come he actually does step up. While this would've been excusable to me before c.113, now that he's in the post-confession dating stage — where he's already (been) kissed (by) his girlfriend more than once — I'd like to see him be more "active" in the relationship even when it's not absolutely necessary. That he's aware that he was being pathetic is good and all, but what's next is to see what's he gonna do about it.
He wants to support Anna? Now's the time. Let's see how. Komaki's one of the better teachers to find them on the roof, but at the same time she's still a teacher. I'm actually not sure she'll turn a blind eye to Anna so easily, so this is Seto's chance to do something.