I voted yes, and said season four, but I'm thinking I should have said season three.
Why? Well, sure, he could've known from the Pilot, but I think it wouldn't really have clicked until he saw Lois covering for Clark too--that Clark had to go away for some reason, and Lois was willingly making excuses for him had to mean that what Clark was doing when he left suddenly was really important. And how much more important can you get than saving people?
"You take turns, advise and protect one another, even heal or be healed when the going gets too tough. I know! That's not a game--that's friendship!" ~Shelly Mezzanoble,
Confessions of a Part-Time Sorceress: A Girl's Guide to the Dungeons & Dragons Game Darcy\'s Place
