The Walking Dead - Season 2 - Interview with Sarah Wayne Callies

Now that Rick knows about the affair, how will that change things between them?
Sarah Wayne Callies: Andy and I have been playing with the idea for a while that Rick has known for a long time and it was a test of whether or not Lori would be honest with him and when and why. It actually opens the door for things to begin to heal for them. He deeply needed to hear her say that she thought he was gone. She wasn't secretly burning a candle for Shane for the last eight years of their marriage.

You say he needed to hear that, but do you think that's the truth? Lori doesn't have any feelings for Shane?
Callies: I don't think Shane ever crossed Lori's mind as anything other than a dear friend until she was in his arms the night that Atlanta fell. There's something about memory that's really tricky, that when you go back to an event in your mind, it can actually change. Lori's having a much harder time putting it out of her mind and putting Shane out of her mind than she ever would've anticipated, given that it was really just a purely physical thing at its inception.

How will Shane react to the pregnancy? Will he assume it's his?
Callies: That's her biggest fear right now, because there's no way to be sure whose baby it is, unless it turns out that she's two months pregnant and it happened before Rick was shot. But at this point, there's no timeline, so she's really afraid. Quite frankly, one of the reasons that she considered terminating the pregnancy is because it has the ability to tear these men apart, and that has huge implications not just to her personal life, but to everyone's safety. There's a part of her that's afraid they might kill each other. This is the kind of thing men kill each other over.

Source: Full interview @ TV Guide