Thats open ending because Naru said 'If only i cant accept your feeling, but i cant' and when he offer handshake Naru ask 'if u dont mind it, can we be friends again' but even if it open ending, it feels like its lead to Seungjoon and Naru ended up together and in author insta, the author makes so many moment of Seungjoon and Naru, and who said 'heol naru is coming' is yunho not Sungjoon and he is not Seungjoon's family, who inside his house and expect pizza is Sora who cut her hair, Mahee and Yunho not Sungjoon, and yeah Sungjoon bit shocked when open the door and see Naru and he said welcome with bright face

spoiler for Only those of u who might want to know if it’s shounen ai or not
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it’s just his black haired friend who loves Naru but in the end naru only wants to stay friends :(