I'm quite confident that Kim Bong-Seok and Lee Gang-Hoon are intended to be potential love interests for Jang Hui-Soo. The recent episode[7], where all three were present, brought an element of amusement to the storyline. While the main emphasis seems to be on Jang Hui-Soo, the interactions in that last episode could easily lead one to interpret that Lee Gang-Hoon is quite bothered by the apparent connection between Kim Bong-Seok and Jang Hui-Soo.
This ambiguity provides space for the idea that Lee Gang-Hoon might have an interest in either Kim Bong-Seok or Jang Hui-Soo. It's clear that Lee Gang-Hoon often finds himself in situations where he's looking after or even protecting Jang Hui-Soo in one way or another. Additionally, we're left wondering about the dynamics between Lee Gang-Hoon and Kim Bong-Seok before Jang Hui-Soo entered the picture.
That's my Personal interpretation of it all. I tried to keep it all rather neutral in my wording.
