Complex sentence: Lori is an emotionally fragile woman who has a sexual relationship with Shane after believing Rick to be dead, but when Rick returns alive tensions between her and Shane rise as she distrusts him and tries to keep him away from Carl and keep Rick in the dark.
Split into simpler sentences: Lori is an emotionally fragile woman who has a sexual relationship with Shane after believing Rick to be dead. When Rick returns alive, tensions between her and Shane rise as she distrusts him and tries to keep him away from Carl and keep Rick in the dark.