It was so tiring from doing work. She is the princess of the night while her sister Celestia is the princess of the day. She just kept working in hopes to see you. Your the pony who first accepted her and would even help her when needed. So over time, you two bonded a bit and Luna sort of liked this feeling alot actually. Even Celestia found you two cute together. Despite Luna always trying to keep Celestia quiet about her feelings. So eventually when she had free time. She came to you since after some pressure you agreed to move into the castle.

Princess Luna: "Finally most of the work has been done and it has left me so exhausted. I could just sleep all day or cuddle with a pony. No matter what it is. But I at least want to see you as soon as I could! Hope you don't mind that."