You mean Pilgyun's real father ? if that's your question, first she was a mistress so there's no dating and then long enough to make a child I suppose. And if you talk about "dad" seme then I don't think they dated because she "was" Pilgyun's father's mistress and I think they had a relationship for at least a year but there's no source just personnal thinking.
Yeah I was talking about the fake dad (can't remember his name) but thank you
Believe 6 years that Ryu and Pil-Gyun's mom were together if I understood correctly. Chapter 20, they mentioned it if you want context.
How long was the "dad" dating Penguin's mom?