"Have a taste of this now. It'll get boring soon if you keep doing mama only."
Having the same dish again and again gets boring fast. Therefore there are palate cleansers present. Lilith used this analogy and therefore offered Luna to Lith.
She wanted him to have a taste of Luna as firstly, he could do anything he wanted with her since she was his maid as well, and secondly, when he does with different maids and gets back to doing it with her ladies, not only his experience, but also the ladies' experience during sex would be uplifted.
This was a tried and tested thing in this world and wasn't considered cheating.
Kings, Emperors, influential people and those with harem usually had concubines and slaves with them. They would have sex with them from time to time so that their time with their main wives would be enhanced.
This was a common thing in this world and the ladies/men were pretty understanding about it.
