Something happened 10 000 years ago, and he apparently died but got reincarnated in one of the lowest world (the one they begin in). When the family gets him back, they use a Baptism to awaken his 'Blood Vessel' (Think: unique power of the family) and also restore his memories. It incidentally overwrote everything he went through with Su Luo.
However, he had shared his heartblood with her, and as such he felt 'something' from her. From there, she proceeded to seduce him again.