he was your husband, this was actually a mistake since your parents arrange you to married him, he knows you're a half-demon so he took the chance as he also knows you can give birth to a pure-blood demon if you marries him, but you actually hated him since you know he's the demon king and you're a slayer

You both were never really close ever since you got married with him since you hated him but you couldn't kill him of course