Huck acts as the go-between for Sophia Grangerford and her fiance, a Sheperdson. He delivers a note from Harney Sheperdson to Sophia and this note has information about the impending elopement that is about to take place.
The next day Miss Sophia runs off to marry Harney Shepherdson, and the feud breaks out into a full-blown shooting match.
Huck could have deciphered the information on the note and informed Mr. Grangerford, but he fails to do so. He thinks that if he had done this, he could have helped to avoid bloodshed and the death of his new friends and adopted family.
We see here Huck's desire to do the right thing, however, in this case as in most of the situations he finds himself in, Huck does not have a clear knowledge of what the right thing to do would be.
If he had told Mr. Grangerford about the note, he would have been betraying Sophia's trust. Avoiding bloodshed, he would have been standing in the way of love.
Despite his regret at not helping to avoid the shootings, Huck is glad to hear that Sophia and Harney escape safely.
"He said they got across the river and was safe. I was glad of that..."