In my game, day 100, people are already starting to defect but it's not in the massive manner you just described.
A few pointers:
1. From what I've heared so far, the best way to keep those idiots, I mean nobles, happy - is to ask all of them who do THEY think should get the fief. Put it in a spreadsheet or something. Then give it to guy most of them said should get it - then he's happy, and the people who supported him don't hate you. The people who didn't support him still hate you, but at least it's more balanced this way.
2. Don't keep lords at all, have leadership score of 30 and run the kingdom by yourself. Throw every single noble you find in your dungeon and rule like a true despot.
3. Bandits do seem to pop up more alot in latter stages of the game. Getting their hideouts SHOULD reduce their number, but keep in mind that their hideouts respawn in time... hmmm... I guess the really weird thing is that even when my force outnumbered and outforced theirs, the bandits never yielded, even when I was charging with Knights against 5 looters, they always stand and fight me. Sounds pretty dumb, and should be fixed imo.