To me, he was watching for a sign that she was vacillating. Some reason for why he should come clean with her and trust her. Accepting Luthor's proposal just wasn’t it. I saw the eavesdropping as an expression of how desperate he was in finding a solution. It wasn’t simply knowing that Lois was engaged but how she acted during the proposal.
See, that's why I enjoy conversations like this: I would never have read the scene that way in a million bazillion years, but...yeah, that makes sense.
I've always kind of thought that Clark had already given up at that point, but yes, if he was still considering whether to trust her, that would explain his presence there far, far better than anything I'd been imagining. I still don't really think the spying is ethically
right (obviously, this stalking/spying thing is just an issue with me) but it does make it seem far less OOC for Clark. So, thank you for giving me an interpretation I can live with.
Betcha can't do it with the Pilot scene, though

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C.