Luna deserves some happy endings. When she gets them, I get that feeling in my eyes like my face is gonna get wet.
Celestia did what she thought she had to do, but even ponies full of love experience a little darkness of their own from time to time. Today, I imagine Celestia kisses Luna awake, and a tipsy Luna nudges Celestia awake.
Luna all smelling like stale hay and sarsaparilla, her mane all disheveled, Celestia's book still open to where she was reading it, her half-filled (half-empty) glass of water, a half-munched carrot next to her. It takes Luna a little while to say her good mornings, and she paces her words carefully, but Celestia knows Luna just likes different things, and she loves her for it.
tl;dr They love each other dearly.