..He essentially went back on our deal and said he could not pay me the percentage anymore.
If any man did that to you, then he deserves NOTHING from you, as far a courtesy, or what is "right" etc.
I judge a man by his word PERIOD, I don't care if this guy offered you the moon, as a second offer - his word ain't worth the breath it took to say the words.
I would give him a two minute notice, backed up with "remember when you screwed me, and went back on our deal" - then I would introduce him to KARMA.
I don't want to hear this turn the other cheek, or don't sink to his level, or be the better man, hogwash, screw this liar to the wall, he's been screwing you for years, and now it's your turn. Do it in style.
Don't worry about burning bridges, this is one bridge you WANT burned.
I'm not going to blame him 100% because you still worked there after he screwed you, so you are to blame for being taken advantage of also. I would have walked after I heard the words Remember our deal, well I'm not honoring it", the next sound he would have heard was the door slamming.
This unscrupulous individual needs a message sent to him.