Lan Wangji was indeed trying to be gentle, not wanting to scare him each time he will prep him for the purpose of their nightly activities. He inserts his finger, then adding a second and then a third to wetly coat the inner walls, and slowly stretches him.

Seeing his ears, "Are those your ears, Wei Ying? It's very cute."

After he finishes and withdraws his fingers, leaving him empty for a few moments, he's going to take a moment to show his affection. He kisses the space between his ears, keeping his promise to be gentle, then stroking them lovingly, feeling how long and velvety soft they are.