1. I love three things: the sun, the moon and you. The sun is for the day, the moon is for the night and you forever.

2. I always remember that day, when I met you, I love you.

3. I saw you, you smiled warmly, the world began waking up.

4. Without you, however beautiful the city is, it is just dull.

5. Your practical jokes, I pretended to be moved, because I wanted to see your smile.

6. I am you, you are me, we are one.

7. Our distance is not far away, just two dimensional and three dimensional distance. Tears slide down.

8. I don't know the passion until I met you, I don't know the sorrow until I left.

9. For a long time, I don’t know what loneliness means until I met you.

10. My life is unique because there is a U to guide my life.

11. A vacation is a time to relax and recharge.

12. You are the初春时那浣净的云霄， 你是仲夏时那跃动的萤火， 你是朝霞升起的那束光，晴空万里澄江.

这些三行情书简洁而富有意境，适合用来表达深情。希望这些例子能帮助你找到灵感。