That's right. Instead of confiding in someone who is more mature and has a mind of sorts, Key is better off saying this to Ryeo. Because it is not impossible that the answer from his other half is
"Think carefully about Key. What about your career? Are you sure it's your son? How will your parents feel? What do people say, "Key?"
and others. That's the kind of thing that Key doesn't want to hear. But a Ryeo wouldn't do the same. I don't know where to get faith from, but that's how Key thinks.
"Ehmm. . . are you ready to hear this?" Key asked hesitantly.
"Eoh, just say it. "
"Promise me to keep it a secret. "
"I promise!"Ryeo answered while raising his hand.
"Ehhhmm, so look, I. . . I. . . impregnated a girl, Ryeo," said Key stammering.
Ryeo's eyes glared in disbelief, and his mouth gaped wide while staring at Key in amazement as he saw a two-headed horse.