Had Lois defended Lex recently
She defended him as a good person after he had both shot and bought her. She believed him over Brigitte Kahn and whatever sense of investigating the issue Clark had developed. When she flat out rejects his attempts to point out problems with Lex like that, what other choice does he have but to not say anything.
He had tried to trust her with details of the investigation, and she had accused him of being jealous and petty and not listened to him at all.
Although, to be fair, Lois maybe was already using Lex as part of an investigation back then, but even her attempt to get Clark to see her relationship with Lex as like his with Cat just does not work. Clark never presented his relationship with Cat as romantic, but Lois clearly was putting on romantic airs with Lex.
