Final answer:
The provided excerpt does not contain enough information to accurately answer why Moira did not tell Johnny about an affair with Roland, as it lacks context about the characters and their situation.
Step-by-step explanation:
The subject of this question seems to center around the motives and actions of a character named Moira in a work of literature or drama. The passage provided does not directly answer why Moira did not tell Johnny about 'sleeping' with Roland, nor does it provide context for their relationship or situation. Analyzing Moira's actions would require a deeper understanding of the characters, their relationships, and the plot of the specific work they are from. Therefore, without additional information or the specific context from which these characters originate, providing an accurate and informative answer is not possible.