Wow. I feel bad for Lana. I hope she and Tim actually do get along, and she's not only with him because she's bitter at Clark. Clark has a good reason to feel guilty there.
The ironic thing is that if he had been mature enough to deal with his responsibilities to Lois, he might have been able to hurt Lana less. He could have told her, "Lois and I didn't realize it, but we slept together that night at the Cabin, and now she's pregnant. I love you, and I wish we could be together, but I have to take responsibility for my wife and child." She would have been distraught, and eventually moved on a stronger person. Heck, he might have even stood a chance of getting her back in five years if he'd done that....
