他是我心里最疼的伤疤
[tā shì wŏ xīn lĭ zuì téng de shāng bā]
This signifies an ex or person who was very dear to them but caused significant emotional trauma. Despite the healing process over time, wounds from past hurt linger in heart and mind - like a healed-over scar which remains visibly as a reminder of old injuries sustained in a relationship.