sorry???

That just as simple as they actually never married and he left his girlfriend pregnant and raise the kid on her own

I'm guessing that at the time they were just dating and not married so he said "I'm her boyfriend", It might be that he got Kwons mom pregnant and dipped

That he was his mom's bf and then he disappeared leaving her and his son behind (for whatever reason) and now that hecame back he expects to see her like sir she ded

Is that who he came to see? The mom? Because he called her one name and then asked to see someone with a different name?

He called for the son (idk how he knew his name) and when the son arrived (the top) he asked for his gf (aka his mother) that's dead

yeah I'm aware but surely 3 decades later you wouldn't be speaking in the present tense considering he didn't even know she was dead

I think it's either they made a promise that he would comeback to her or that just his desperate and shameless self, hoping for her to still acknowledge and continuing their relationship