They were originally planets in their respective orbits, but due to some mysterious fate, they collided into each other's light.
Who has his pride broken for whom? Who let go of their guard for whom? Who has stars hidden in his eyes when he looks at whom, and moonlight is wrapped around his fingertips when he misses whom?
It's unclear, the way is unclear.
All I know is that the sight of them standing side by side when the winds in the six realms are moving is more touching than any words of love.
As for which two stars are most compatible?
Hush - the answer is hidden in the wind that turns every page.