Why does this feel so bittersweet? ;_;
This is what I got out of it: Kotori was at least somewhat still in love with Honoka, and that's why Nico congratulated her for making it through the wedding without making a scene or crying more than is normal.
Nico and Kotori are living together, maybe just as roommates, maybe friends with benefits, and Nico's gradually fallen for Kotori. Kotori's confession to Nico in this scene is expressed somewhat facetiously, so Nico doesn't trust it or take it seriously.
And now, after the wedding, they're going to go home and Kotori is going to forget about the wedding, probably by doing something with Nico. Meanwhile, Kotori's confession is still up in the air, because Nico still doesn't know how seriously to take it.
I think that's the bittersweet quality.