曾以为眼泪的温度烫伤心脏
[céng yĭ wéi yăn lèi de wēn dù tàng shāng xīn zàng]
Translating to 'Once thought the heat of tears could scald the heart', it portrays a feeling where they once felt tears caused so much sorrow or hurt as if they've been scalding their heart.