AyaDuu might have come first though.
There was a cryptic Pocket Morning answer from Haruna a while back saying that her special friend was talking to someone else and that she was jealous.
So, even though I suspect that both pairing are "business", the narrative I have for them is:
Production for Lilium starts, separating Ayaka and Haruna.
Haruna starts flirting with Haruka (her love interest in the play?)
In a rage, Haruna turns to Erina and HoneyPon is born.
Sayuki catches wind of this and breaks up with Haruka.
Now, Wota CSI might come up with more evidence and refute this theory, but for now, this is what I am going with.