Chaos, I haven't had the opportunity to see the movie yet (it hasn't opened here in Sweden), but I have skimmed through the novel, read the prequel comic and seen the two Christopher Reeve Superman movies that are being used as prequels to this one. Also, I've read some interviews with Bryan Singer.
The impression I get from the Christopher Reeve movie Superman II, as well as from the novel and the prequel comic, is that Lois in all probability only made love to Superman once, and she doesn't remember that time, because Clark took away her memory of their night together. (At the same time, he took away her memory of his own double identity.)
If you've got the comic, I'd like to call attention to a page spread where Lois remembers five times when Superman rescued her. The first rescue, where Lois is half buried in her car (and where she's actually been killed - Superman turned back time to bring her back) is taken straight out of the first Christopher Reeve movie. I don't remember anything about the following three rescues, and I suppose they are used as generic examples of Superman saving Lois's life.
But the last one, where Superman saves Lois from drowning in the Niagara Falls by flying her away in a boat, is hugely interesting. In Superman II, Lois really did jump into the Niagara Falls to force Clark to change into Superman right in front of her and reveal his secret identity. Lois's attempt failed, however, since she was swept to one side and brought ashore by the current, and Clark never did have to be Superman to save her.
However, straight after this Niagara Falls incident, Clark accidentally revealed his Superman identity to Lois, and he flew her to his Fortress of Solitude where he gave up his powers so that he could make love to her. Later, however, he had to get his powers back, and he gave Lois amnesia so that she forgot about their lovemaking and about Superman's double identity.
Now consider that picture of Superman rescuing Lois from the Niagara Falls by flying her away in a boat. That's a false memory, a planted memory. It's also the last memory Lois has of Superman saving her before he disappears. To me, this strongly suggests that the comic book acknowledges the fact that Superman tampered with Lois's memory (apparently to make her forget about their lovemaking and about Superman's Clark Kent identity). It also strongly suggests that Superman left the Earth almost immediately after this lovemaking/amnesia business, since Lois has no memories of Superman rescuing her after the Niagara Falls incident.
So we have a situation where Lois presumably had sex with Superman only once and where Superman took away her memory of that night and disappeared almost immediately afterwards. We have, at least, a situation where Lois doesn't know that she and Superman were ever lovers. She does remember that they had a special relationship, but both the novel and the comic make it clear that Superman left the Earth without saying good-bye to her. (Presumably he made some sort of announcement before leaving, so that people knew he hadn't just been killed.) Lois must have felt jilted that he would disappear without speaking to her. She may have felt that this was his way of saying that he didn't want her any more.
Bryan Singer has said, in some interviews, that he wanted this movie to say something about the way that families have changed and marriages and relationships aren't so cemented any more. There can be no doubt that this is the reason why he brought Richard White into the picture (remember that Lois's relationship with Richard was Singer's idea). Also, it was perhaps necessary to bring in a man who could at least theoretically be Jason's father.
Of course... there is one thing here that does not make sense. Apparently, in the movie, Lois sees Jason using super-strength. She must have realized that Jason is Superman's son, and yet she doesn't seem to react!!! Why not???? Did she already know about Jason's paternity after all? If so, why hasn't she spoken to Superman about it?
I guess only the sequel can answer these questions.
Ann