Considering this, does Lori tell Rick about Shane?
There was not a large span of time between her time with Shane and then Rick's return and her time with Rick. In the concluding sequence of the episode, Lori admits to Rick that she had an affair with Shane in the belief that her husband was dead.
Subsequently, question is, why was Lori mad at Rick for killing Shane? The reason behind this was that Lori had gotten fond of Shane. Now when Rick returns back and Lori found out that Shane had lied to her, she got really angry and upset on him but there was a part of her that was telling her that she and her baby might not have survived if Shane wouldn't have been there.
Consequently, did Lori Love Rick or Shane?
Lori is definitely having problems with the fact that she has feelings for Shane. She definitely loves Rick and possibly has stronger feelings for him but this is a guy who very much part of their family before apocalypse and was pretty much all that was left.
Did Lori cheat on Rick before apocalypse?
Simple. She was cheating on Rick far longer than just the end of the world. If it was the show there's a solid chance she feared her baby belonged to shane and wanted to abort it, so your theory stands! I'm pretty sure the show confirmed that it's Shane's baby.
