I realize that I'm speaking as one whose "mental image" of Lois and Clark has been formed by the comics and movies, not by the TV show. But to me, it is easier to imagine Clark falling out of love with Lois than Lois falling out of love with Clark.
Consider the Smallville TV show! That show is on its tenth season and Clark has been in love with Lana and made love to Lana and what not. And
now the producers are considering pairing him up with Lois. Maybe.
And in the movie Superman III, the sequel to Superman II where Clark first made love to Lois and then took away her memory of what had happened, Clark was sort-of-flirting with Lana.
In the comics in the nineties, Clark decided to risk Lois's life rather than commit a crime, and afterwards he seemed to grow tired of Lois. Even though he was engaged to Lois, he flirted with his old flame, Lori Lemaris the Mermaid.
Here is a panel from a comic book story which I read as a kid:
Superman is kissing Lori Lemaris! Oh no!
And his relationship with Wonder Woman always bordered on being romantic.
Lately Lois has been seen having boyfriends too, Lex Luthor in LnC, Oliver Queen in Smallville and Richard White in Superman Returns. But she never had any boyfriends in the comics I read as a kid. Back then, Superman was her only love. That is why I think of Lois as being more devoted to Superman than he is devoted to her. That is also why Becky Bain's Ad Astra Per Aspera resonates so strongly with me. Clark has married another woman and abandoned Lois - certainly out of a sense of duty, but still - while she keeps loving him and loving him, even though she eventually, after eighteen years or so, marries someone else.
But if we just consider LnC, is it true that Lois would fall out of love with Clark more easily than he would fall out of love with her? I can see one reason for thinking so, and that is that LnC Lois has had relationships with men before, while Clark was a virgin. Otherwise LnC Clark and LnC Lois seem pretty "equal" to me when it comes to loving the other one. Those of you who think that Clark's love for Lois would be more steadfast than her love for him, what do you base your opinion on?
Ann