Why is Huck’s “confidence in the human race well- nigh obliterated?”

Huck felt that Tom betrayed him..... he broke their oath. This was something that Huck had never dreamed could happen.

The poor fellow had got the attorney to promise secrecy, but what of that? Since Tom’s harassed conscience had managed to drive him to the lawyer’s house by night and wring a dread tale from lips that had been sealed with the dismalest and most formidable of oaths, Huck’s confidence in the human race was wellnigh obliterated.