I didn't see love in Nanjo eyes. Nor some signs of affection. He wasn't flustered at all ...

To be fair it's not the first time Mokyeon says he likes him, maybe he got used to it? But yeah Nanjo's smile doesn't feel completely true to me, maybe he still wants some sort of revenge, maybe he's only in it for the sex, but if he is I think he's in denial about the feelings part or he decided that he simply doesn't want to think about it. Because if he doesn't feel anything for Mok then he simply wouldn't have stayed there. There's a lot of disparity still, considering Mok is now realizing just how deep his love goes and this might be the main conflict going forward.