Eriha definitely thinks 'Naoya' belongs only to her. Everything from asking to hand something to Naoya for Nonoka without seeing asked, being the only one calling him Naoya at all times, to going out of her way to set Nonoka up with an ikemen because she can't accept Nonoka having a crush on Naoya. Let's not forget this ikemen was nowhere in sight when eriha knew Nonoka was trying to find a bf.