I am quoting from The Return of Sherlock Holmes, The Second Stain, by Arthur Conan Doyle:
“Mr. Holmes, I will tell you everything,” cried the lady. “Oh, Mr. Holmes, I would cut off my right hand before I gave him a moment of sorrow! There is no woman in all London who loves her husband as I do, and yet if he knew how I have acted—how I have been compelled to act—he would never forgive me. For his own honour stands so high that he could not forget or pardon a lapse in another. Help me, Mr. Holmes! My happiness, his happiness, our very lives are at stake!”.
Here the meaning is pretty clear. I suppose the word 'lapse' means 'a slip' in this sentence, but it seems to me that the sentence could have ended after the word 'lapse' and it would have been fine.
What is ‘another’ doing in this sentence and what does it refer to.