I don't know why everyone is calling this a "love triangle" when it is clearly not. Long-haired girl even said it wasn't on page 9. I don't know if it will turn into one, but just the fact that they have an honest 3-way relationship makes it less likely just by showing that the writer is aware that more than two people can be in a mutual relationship at a time. OTOH, the title
is short for "Fetish Couple".
@Chet31 I'm pretty sure all three characters are in their second year of high school and are the same age. The short girl is just short. She is also wearing the same uniform as the others, just without the jacket; she has the same shirt, the same bow tie, the same sweater vest, and the same skirt. Also they are all hanging around in the same school. The change in description ("second year" vs. "second year of high school") may just be because the translation group had the same interpretation as you—the editor's note even called Hayase a "lolicon".
@Jackist Giving this series a shitty rating for this one chapter seems rather harsh. Give it one for that last shitty arc instead.