I haven’t finished the whole novel yet. There are 300 something chapters and I’m only on 183 (and I’m translating on my own now since the Eng. translations aren’t as far). So I can only answer with the knowledge I currently have.
The man from the past in his flashbacks is his teacher and mentor. He’s the one who’s cursed the MC with immortality.
The ML falls for the MC while getting close to the MC to convince him to join him in his cause… he doesn’t realize it’s love for awhile, but he falls first and he falls hard. I’d say he’s a green flag in that he treats the MC well despite manipulating him for his purposes early on, but he does have… interesting thoughts sometimes lmfao. He’s a little twisted internally but he’s sweet with the MC. There’s no second ML so far.
I don’t know yet!
OK, so I just finished catching up with the English translations for the novel. Hands-down, this is my favorite Korean novel I’ve ever read. For those asking about the ages, the MC is “about 200 years” old in a body that’s physically 18. The ML is 26 officially, but could be a few years younger (he doesn’t know his exact age). Both the main character and the male lead are characters that were clearly made with love—neither of them are typical for the genre and they both are strong with softness at their core and a tragic backstory wrapped in mystery. Buckle up. This one is going to be good.