Responses

it would be possible that this guy was invited by someone else or that he just went without invtation

I watched a lot of korean dramas, it seems they just invited a whole department to their wedding. in my country too, its a common thing to invited your high school or university buddies eventhough you barely know them, sometimes you just need one invitation, just like when you invite an alumnus to reunion party.
Okay, so now it looks like maybe Sun Hwa thought Sunbae had recorded him and let the recording out, and maybe that is what bothered Sun Hwa most (more than the pressure, abuse, and choking). That explains dropping out of school and becoming a recluse. But why would Sunbae stay friends with the homophobic hater and invite copycat to the wedding?