I'm most confident in saying that Ki Ho is definitely Bo Geol because the actor is the main lead, and the encounters that happened in their young age, mostly associated with the love story, should revolve around Ki Ho. Even though they were just friends helping each other in their youth, this aligns with the director's perspective.
As an audience, Bo Geol's personality is more similar to Ki Ho's, while Woo Hak's personality doesn't quite match Ki Ho's.
What's intriguing is why he ignores Seo Mok Ha. If he were Ki Ho, he shouldn't have amnesia, especially in the first episode, where he keeps going to the location where Ki Ho and Mok Ha were supposed to meet. His repeated visits suggest that Ki Ho hasn't lost his memories, which makes me believe that Woo Hak is definitely not Ki Ho, in my opinion.