Revealing Leia to be Luke's sister was an act of genius, because it allowed the love triangle to be resolved while not only NOT making Luke a cuck, but making him an anti-cuck. By Return of the Jedi he had that on lock. He could have had Leia anytime, anywhere. Then he bowed out on a technicality, undefeated, and retired as a volcel monk with bragging rights that the only girl he ever made out with was his own sister. This is what is referred to in Joseph Campbell's schema as the "Master of Two Worlds" stage.