Everyone is reborn, it's part of the cycle, the circle of life. Some happen to retain their memories, Jin is one of those lucky few. He remembers soft smiles and warm hands, he remembers his long list of dad jokes, he remembers soft mornings, waking up to a mess of bodies. He remembers six lovers and it hurts to know he'll never meet them again. He had resigned himself to this thought before he even took his second first breath.
The day he gets his soulmate mark the agonizing loneliness makes itself aparant, thrashing and clawing it's way into his strained smiles. He remembers his six lovers from a past life and he wishes (not for the first time) that they were still here. (He wishes everyone could remember their past lives, for he was greedy and wanted the comfort from the memories he had grown up clinging to.)