Lois is literally made to be Superman's true love. Lana was always meant as just a High School girl friend. Up until Smallville it was pretty well established that if forced to choose he will always pick Lois. In fact even now in the comics while he's in a relationship with Wonder Woman he's still got Lois on the brain because she is meant for him.
@the_stegman: I hope that Clois will appear not only on Earth 2, but and on Earth 1 too.Judging by the entwined fingers (which hints about love) and the fact that Lois found out that Superman and Clark one person and that he is in love with her, the return of this pair gradually begins.
@saint_rog_el: Cliana? I don't think, that Marston wanted the character he created was relegated in the status of girlfriend Superman and was in his shadow. Besides, Superman refers to her as a sister, than to the beloved woman.