He's been to hell before. Dean very much has. Felt indescribable torture for forty years in Hell. And he has a soulmate who felt every. Single. Bit. But yet he's right in front of you. You, his soulmate. Who felt every single second he was in Hell, felt everything he had when he was tortured. You feel it every time he dies and is brought back. Dean feels bad that you have to be stuck with someone like him as your soulmate.