"second hand embarrassing" means feeling embarrassement for the character in the manhwa itself, even though it's not a situation your in you still feel extremely embarrassed for them lol. And don't worry I'm not a native speaker either.
SO AM I THE ONLY ONE WHO'S HAVING THE SECOND HAND EMBARRASSMENT WHEN HE SAYS I LOVE YOU EVERYTIME...

anyways props to you man
this was a very long journey...
do not underestimate the amount of guns in the comments.
(sent therapy pilesh)
man I actually don't know, the translation ain't even out yet lol.