I half expected Ria to say, "I am fine being your second girlfriend."
It may have been the case where Suzuka knows Haruka and Ria have something mutual, and she was the one who took the opportunity to confess while Ria is away, knowing Haruka wouldn't have the heart to deny a confession.
So far the only boyfriend thing Haruka has shown is getting Suzuka a gift for their anniversary. For the most part, the Haruka that has been shown is more like someone "acting like a good boyfriend" instead of someone who is deeply in love with his girlfriend.
Haruka being lustful towards Ria may have been the turning point in which Ria thinks of her body as an asset rather than a liability - will have to see as to what got her to become a model to begin with.