To restate her soliloquy, Lady Macbeth is saying that it would be so much easier to be the vicitm rather than the killer(s). If she was the victim, she wouldn't feel anything. However, being the murderer, she must live in doubt and fear until she dies or until she is able to get away from her guilt over time.
Act III, scene II Macbeth thinks that there is still more to do. Although Duncan is dead, he fears Banquo's sons, who will reign some day according to the prophesy. "We have scorched the snake, not killed it" supports that. Lady Macbeth doesn't want to hear about Macbeth's brooding over Duncan's death. She tells him to be "bright and jovial among [his] guests."
Macbeth admits to his wife that he's worried about Banquo and his sons, but he never says what he's going to do about it. His plan will be the murder of Banquo, but he never shares that thought with Lady Macbeth.
Lady Macbeth is concerned because she sees that her husband is worried and she asks him why he is so worried. She says that they should be enjoying their position as king and queen but Macbeth does not seem to be enjoying his reign. Macbeth tells her that he does not sleep well, or much at all, because he knows that their position in the court is not secure. He knows there are forces out there waiting to destory him and he's determined to ferret out those forces and get rid of them. He's becoming paranoid and desperate. Lady Macbeth tries to soothe him and reminds him of their banquet that night. Macbeth admits that he is upset and worried about Banquo and Fleance. He thinks Banquo suspects him of killing Duncan and he doesn't want Fleance or his descendants to become kings as the Weird Sisters predicted. Lady Macbeth again tries to calm him by saying neither Banquo nor Fleance can live forever. Macbeth then says that he does have a plan regarding those two but he doesn't want to share it with Lady Macbeth just yet. He tells his wife to wait until the deed is done and she will be pleased with the results.