I feel like the soul mate/lover that Biwan saw once in a vision wasn't meant to be Seoho in first place, but Minchan. They have the same face, so Biwan met Seoho first and thought that was him. Minchan is still sort of Seoho in part plus Minchan himself (since there are two pieces of different souls mixed together), but even so, Minchan is his own person. He being his fated partner doesn't change the fact that Biwan fell in love with Seoho first, so even if he decides to protect Minchan existence and recognize him as his fate, it would still be so damn painful to give up of Seoho. He must have decided do that even so and that must be why he's crying
I feel like the soul mate/lover that Biwan saw once in a vision wasn't meant to be Seoho in first place, but Minchan. They have the same face, so Biwan met Seoho first and thought that was him. Minchan is still sort of Seoho in part plus Minchan himself (since there are two pieces of different souls mixed together), but even so, Minchan is his own person. He being his fated partner doesn't change the fact that Biwan fell in love with Seoho first, so even if he decides to protect Minchan existence and recognize him as his fate, it would still be so damn painful to give up of Seoho. He must have decided do that even so and that must be why he's crying