You are going to think that I am crazy, but I am going to talk about sense of smell.
Humans do not realize how much our actions are affected by smells. Smells can bring back memories, and smells can control our hormones in many ways. (I won't go into detail on one of the examples because you would all say Ewwwwww!)
Smell plays a part in sex. I don't know how it meshes in with pheromones, but you often hear widows comment that they have kept their husband's possessions around because they can still smell his scent. (Lois has probably done that in a couple of NK-themed fanfics.) We are also biological creatures, who react to conditioning. So being close to your lover/spouse and smelling them, even unconsciously, can trigger arousal.
So it would be reasonable that Lois, being close enough to Clark to smell his body, would react by being aroused. There is also probably some unconscious conditioning having to do with the sight of him too. After all, she is not going to fall into bed with every good-looking man she sees. But she believes they have already been lovers and she has gotten the visual and olfactory (smell) triggers that have brought her to arousal in the past (even if she did not complete sex in the past). As some previous posters said, her body remembers him.
Also, Lois, without her memories of Clark, does have other memories of the past. And her memories of past relationships fall into the category of "men only want one thing." So she assumes Clark is the same as the others, and would not realize how deceiving him into sex would hurt him.
So I don't see this Lois as any more conniving than normal Lois, the Lois who sees nothing wrong with using her lockpicks whenever possible.
I also don't see Clark at fault, because at the time they have sex, he DOES believe that her memories of their relationship and her love for him have returned.
On your original question, ML, a couple of other posters have already posted my opinion. Our memories shape us but they do not change who we fundamentally are.
