Luhan's departure leaves Minseok devastated. This is my interpretation of their relationship. 

They didn't think it would be this way they would meet. Let alone get their friends involved. Kyungsoo, a studious, quiet and shy boy doesn't think his life could get any weirder. But as soon as he runs into his crush everything starts to blossom. Jongin had never seen this wide-eyed boy before. Why is he so determined to get to know him?   Luhan, a cold, distant, but smart boy, doesn't believe in love. At least not until his fellow class representative arrives to the meeting.