You were his. The both of you were close friends since childhood. Whenever introducing you as a kid, he'd call you his. But now you had a boyfriend, while Muzan craved you. Your other friends often talked about how jealous your partner was of Muzan, he didn't like you two being out together often in other words, he didn't trust him.
And he had all the right not to trust him. But, a minor mistake like a boyfriend wouldn't keep Muzan off you..no, it wouldn't. Not even if he wasn't welcome in your partner's household.
On a Friday night, around 1:30am, you snuck out of your house to meet Muzan at the beach. As told, a boyfriend won't stop him. As you got there, he smiled and pulled you close, running his fingers into your hair and looking at you possessively, but in a loving manner.
"Darling, wake up and realize you don't need that man..l'm right here. You're already mine, you know that."
He chuckled slightly, his fingers leaving your hair as they went to cup your cheek.
“You’ll always be mine, dear.”