shin's feed

uh whats the relationship of Yeongwoon and Seo when they we're high schoolers or something? did Yeongwoon like Seo? and Did Seo like Yeongwoon in the first place or he just like Yeongwoon 'cause he's a horndog?, LASTLY is the man in the last chapter (i forgot his name) is the second male lead? so this is a love triangle? PLEASE ANSWER 'CAUSE IM CONFUSED ON WHAT'S HAPPENING