As for guy abandoning you, I don't think most of the relationship dynamics have been implemented.
It sure isn't. It seems that relation has nothing to do with it.
I decided to declare war on Sturgia by myself and form my own kingdom.
I conquered cities and castler from west to east. Recruited some lords/clans from sturgia. None of them brought any fief with them.
And then I've captured Sibir.
Gave it to Lord X.
In a few days Sibir turned red and the Lord X betrayed me back to Sturgia.
I then recruited another Lord Y, took Sibir and gave it to Y. Afterwards I've invested all my influence points to promote all clans to 70-80i, reaching up to +80 relations. And yet Lord Y betrayed me taking Sibir. Again.
So I finished the war in a week.And then met this Lord Y (neutral sturgian) in the field, recruited him. Again. And he did not bring Sibir with him.
It's a bit frightening to give some lord two fiefs now. Risking to give it back to your enemy in a single moment without a single blow.