i don't see any + points in the romantic scoring with a Layfon x Nina duet.. well as i see it all scenes are just like "senior & junior", "friends" or "superior & subordinate"
as for the Felli x Layfon duet.. i see that well, Felli slowly, gradually falls for Fon-fon.. she learns to get jealous, scolds Fon-fon when he does wrong.. etc. etc.
i still go for a Felli x Layfon duet.. i find it cute and well..interesting.
either way..everything depends on Layfon to finally "feel" affection from any of the girls in the anime.