You never lost anyone in the first place because they were never a friend. Be happy to have flushed the toilet, the odours of bad character corrupt a good spirit.
There are plenty of people like this in the world. With experience, you get better at spotting them. Most of the times it is not worth the battle because fools can battle nonstop because they have nothing better to do and they thrive on the misery they bring. Toxic environment, caustic air.
But on a bigger scale of things, it is better to say no to what doesn't feel right. Money can't buy sanity and most people who are douchebags end up losing it one day. What comes around goes around. Every time.