
Marriage of convenience. And the reason why we won't know what happened to the young master after Hosik's death is because the current Hosik is the one viewing these past memories. Therefore, he wouldn't know about what happened after his past self's death.
The young master never loved her and never would as Hosik was his only love. That was why the wife was jealous and the mother would never send him away. I do wonder what happened after Hosik's death. The young master seemed like the type to either (a) become a living shell or (b) commit suicide along with his love's body.
B seems more likely to me since he doesn't have any attachments to anyone else aside from Hosik. Hosik was the reason he even went on to conceive the child, and as you could see, he wasn't keen on the child's existence because he (the child) was no part of Hosik. His face said it all when looking at the kid and looking at Hosik joyfully hold it.
The past him wanted to be with Hosik and start a family so desperately that when their souls were able to meet again in present time, the otherwise straight him fell in love. Insanely in love.
Spoilers about the characters in the past:
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I am left with so many questions. What was the young masters life like, after Hosik passed away? Was he able to be happy with his wife? Did he have any feelings for her, or was it just a marriage of convenience? It just ends with Hosik passing and we dont know what ends up happening to the young master.