How early Cat knew about Chow's other girlfriend? When he told her about it the night they eloped. (More on this later).
So Cat di not realize she was acting as a cover for Chow's other girlfriend.
CAT: “I’m over him too, Clark. Please, I’m fine.”
JOHN: I think she protests too much.
A bit.

about lousy reasons he left Lois open to Dan's attacks.
Um... computer expert? Spent all day playing on Lois's computer? Would have found it if she had.
I guess that makes sense.
I hope they can link it to Lex.
Wouldn't that by nice and tidy?

Hmm, if this story did nice and tidy it would not be so long.
I'm going with "ruse" to get Eugene to be the scapegoat for Harrison's murder.
I figured it was too. It seemed the whole Eugene/Lena setup was part of a grand plot to have Eugene charged with murder.
I figured it couldn't only be Claude's fault that she wanted to wait until marriage.
I guess I always focused on Clark being the main force behind waiting, but actually from the dialogue in "Virtually Destroyed" it does seem it is largely Lois' idea, although in "Super Mann" it seems it is Jimmy's fault (at least Lois and Clark were making lots of progress before Jimmy returned with his not all that helpful observations).
Lois knew something wasn’t right. Clark should have been here.
JOHN: Why, Cat told her he was helping with an emergency. There are all sorts of reasons why he could have been delayed.
Psychic feeling.
I guess that makes sense. Since she does not know their source this might work against Clark more in the future.
She doesn't really mean that. What else is she supposed to say when a detective notices she has an expensive looking watch? I got this from one of my sources?
Why not, it is not illegal to accept gifts from sources.
I got this from this guy I'm investigating?
Clark:Better than calling him a friend. Anyway, she could have at least used the more neutral term "acquaintance".
Lois is just panicking here and Clark's an easy target. Lois tends to blame Clark first until she has time to think about it. He did lie (and still is) to her about being Superman, so maybe he would do something like this to teach her a lesson about breaking the law.
Clark:Not after I swore secrecy on the lives of our grandchildren.
Lois:What makes you think we will have grandchildren.
Clark:Lois, you are the one who said "our".
Lois:

O, I forgot I said it that way.
Or maybe someone at the office overheard her and Clark talking about Eugene?
At least in canon they did it totally in the open, so that was entirely possible. I really think they were way too open with lots of what they said in canon.
Must not have been a very detailed search.
They didn't seem to spend much time looking in canon either.
Hiding on the ledge really should not have worked.