There could be two possible outcomes
First. Sungyeon could be lying about all this amnesia thing, so he could test or observe hosik (not sure). That's why sungyeon is always looking at him.
Or second. Sungyeon actually lost his memories. He keeps looking at hosik because he's curious about him and their relationship to each other, cause I'm sure he's wondering if hosik is only his junior or they're is actually something between them
Ms. Kim will forever be the