Possible side story lore for Na-in and Boss

I might be reading too much into it but the scene where the Fox and Geumryang are at the jewelery store to buy a ring kinda stuck with me. there's this part where their talking about reincarnation and past/multiple lives which idk the Fox's response kinda hints to it happening before. Which maybe is also why hes always around Na-in, I mean Na-in is very obvious in his flirting and treats him as a partner. Like seriously they even live together so im assuming the Fox knows him through a past life and Na-in may be unaware.