I think the pretty guy is responsible for his ex lover death. The relationship with minhyung(person pretty guy is with now) with the green eye person, I think is one of two things. 1. green eye is jealous of him probably not thought or 2. Minhyung is super toxic and something bad happend to pretty guy and pretty guy forgave him and green eye did not. I think the pretty guy relationship with the ex lover sister (minjoo) is that she gave up her crush for him and since the pretty guy is responsible for her crushes death and plus her brother is dating the pretty guy that have a pretty awkward relationship. If this doesn't make sense I will make a clear version.
Jamien the main character has always liking a liking to pretty and cute items, and he is often misjudged for his appearance. Then one day while he was working at the cafe he saw the guy (forgot his name) and wanted to touch him because he had token a liking to him. But the "pretty guy" was already in a relationship with someone. The person who is dating the "pretty guy" want him to become his lover. But the pretty guy only wants a sex partner. The pretty guy has some guilt for something (we don't know yet). Jamien fall in-love with the pretty guy, it's like love at first site. And the pretty guy wants to mess with jamien. The guy working at the cafe/jamien friend and the guy the pretty guy is dating are different people any-other confusing thing reply to me and i will answer them.