Will somebody please remind me how the pheromone worked again? I always thought that it lowered natural inhibitions and brought out the animal attraction in the victim. So I cannot see Lex falling in love with Lois because he was affected by the pheromone. The attraction has to be already there. Miranda tried to use it to get Luthor to fall for her, but it didn't work.
Besides, his obession is not due to the pheromone. I don't think he was sprayed with the 100% concentration. As I remember, Miranda sprayed Luthor with the pheromone at close range, so she couldn't have used a 100% formula. In the script, there's a scene when Luthor "wakes up", and recalls what had happened when he was affected by the pheromone, and realises that the city is in danger.
And the final scene, when he was burning money, I felt that he was totally rational. After being affected by the pheromone, he realised that he found Lois Lane attractive, and he (in his own perverse way) loved her. He was not too happy about the realisation. "No, Nigel, I'm really in love. I'm doomed." I mean, nobody plans to fall in love. I think that his obession with Lois Lane was his way of loving Lois.
I see this scene to be parallel to the situation with Lois and Clark. Lois is not too pleased to realise that she finds Clark attractive.
We can establish that by "Pheromone, My Lovely", Lex Luthor has already fallen for Lois Lane. Of course, the interesting question would be, if Superman had not shown interest in Lois Lane at the beginning, would Lex Luthor have spent enough time with Lois Lane to fall in love with her by the time of Pheromone, My Lovely?
What do you think?