那段情誓死难忘那份爱刻骨铭心
[nèi duàn qíng shì sĭ nán wàng nèi fèn ài kè gú míng xīn]
This conveys the notion of undying memories of a certain love affair, emphasizing that the emotions tied to that experience are deeply engraved in one’s heart, suggesting both beautiful and possibly painful recollections of a significant romantic episode.