Personally, I find Clark's sulky, prickly behaviour more believable than Lois's - although the reason I do is largely because of the foreword to this section, which reminded me that his illness is making him lose his usually sunny, patient attitude towards Lois's foibles. I think it would be worth trying to include that reminder in the story itself from time to time. You've done a little of that already, I know, but I think it could stand more of the same. Give him a headache, for example, or make him tired and crotchety - you did that very well earlier in the fic when he was hiding his illness from everyone. Alternatively, have other people reflect on the change in his behaviour - Perry, say, or Jimmy, or Clark's parents. Oh, and I know it's a fine balancing act between turning Clark into a rather wet, pathetic creature who's always sick, and keeping him resolute and strong, but I know you can do it.
I struggled with Lois a bit. Yes, I can believe she's temporarily lost sight of why she's doing all this in the first place - being married when you really didn't plan to get attached yet will do that to a person, especially Lois. I'm less sure that she'd play away with Lex once she was married - although the result was some fantastically tense scenes between her and Clark. Lois does things wholeheartedly, with absolutely every ounce of her commitment and energy, doesn't she? Sneaking off on the side with Lex seems a little unlike her, to me, especially when her husband is ill. The last thing I want, as you know, is a soft, cuddly Lois who is nothing like the character we met in S1, but even S1 Lois had a strong moral code which I don't think would include extra-curricular daliances with Lex.
However, I'm willing to wait and watch the story unfold further. Who knows? Maybe I'll change my mind on Lois.
Oh, and I'm very glad she told Lex immediately without having dinner with him - that much, she got completely right.
Yvonne