It can be one of the most annoying and hurtful of situations. Having to ditch someone because they constantly ditch on you. You invest so much time in these friends to figure out at one point that they are vile serpents. It isn't that difficult to remedy the situation.
IGNORE. God says to be wise as a serpent but harmless as a dove. These confrontational people have so many issues that nothing but the blood of Jesus will fix them.
I realize that each year, my circle of friends I had get purged, and often replaced by new more awesome people. But even if not, I'd still rather quality over quantity.
The best advice I can give you is to not give an announcement as to your plans. With some people there are non-negotiable terms involved....FLEE!