I've cut out people who used to be good friends after they showed their true colors. It's almost always because they are selfish to the point of hurting others.
The worst was a friend I grew up with, and stopped others from kicking his ass multiple times in High School and in our early 20s. He talked me into working with his family's company, which did technology for the California State Government. The business was doing well, and I made some big deals that really set them on a great path in a two-year period. Instead of them taking that path, the family internally all fought for the $$$ without the staff knowing it. Huge new homes, nice cars, big vacations, etc, and as I had a newborn looking for a new home in the area, I found out from one of my biggest customers that my "friend" has started a new company behind everyone's back and was soliciting them, because the family company is going to fail/go bankrupt. I am stunned at the news from my customer, because I know of the multi-million $$$ deals I delivered. When I confronted the asshole, he offered to let me come work for him and his new company. GTFO. I told his family of his plan to gut the business, and what did the dummies do? They let me go... with a newborn and tons of success for them. The company proceeded to fail, as did his new start-up. I cut him off for good, and looking back, my not allowing him to get his ass kicked was a disservice. He needed it badly. I may see him again after two decades next month as I travel to NorCal for an event with some mutual friends... and if I do.... I'm going to have to walk away.