我以为你百毒不侵我以为你刀枪不入
[wŏ yĭ wéi nĭ băi dú bù qīn wŏ yĭ wéi nĭ dāo qiāng bù rù]
It reflects disappointment after realizing that someone you thought was emotionally invincible (immune to harm) has actually shown their vulnerability. The phrase means 'I once believed you were immune to any poison/invulnerable to any attack' but later found out that they can be harmed.