i have a hunch that they're fated pairs. Ive read many omegaverse with this concept and the first thing that attracts them are with pheromones. Taeju and Euihyun have the same scent and taeju's scent have a calming effect to euihyun's body even though they just met (during earlier chapters) during his suicidal days. Plus, it is impossible for euihyun to be vulnerable to Taeju's scent unless his senses are already familiar with it or if they are fated pairs.