At this moment of the series, I still don't see the MCs as love triangle. Koto loves Aya, Aya loves Koto, and Erika loves Koto. So it's currently just Koto-Aya love relationship with Erika watching them.
Erika is good and the most reasonable one here, but hopefully she can get over and find herself another love or target in life, since 7 years have passed and all Koto's feelings are towards Aya.
For Koto and Aya, their relationship is vulnerable, but they surely love each other (even when maybe they are too invested in the ideal image of each other, but I can feel that they truly love each other). So I hope that they can figure it out and be happy together.