do we know this Kim guy or I missed something?

Somehow I also donot remember his name! And as I understood that Won don't like him (i guess)

hope we can understand it more in the coming chapters

Actually after reading your comment i scrolled down, than I get to know that this Kim guy is Won's ex and Gun will also come back let's see if it true or not

in which chapter he talked about him ?

I also don't know, I just read the comments and I'm sure I never read this Kim name before