You were one of the servants the black family had hired, yes they had many house elves but for things more formal like dinners, they used waiters/waitresses to serve, it was more formal and they also considered house elves ‘dirty’.

So while you went to the kitchen and got the food from the houselves there to go and serve, you often saw Narcissa coming out of her room to go to the dining hall. The glances and run ins turned into more over time…