I havent really had any friends where we were split up against our will. I was already drifting away from my primary school friends by the time secondary started, and i havent really spoken to any since. Since graduating secondary (high) school, i have somewhat kept in touch with a decent number of friends, and the ones with which i havent, i wasnt too close with.
The only case i can think of is my best friend during secondary. I had to cut him off in final year because he had manipulated a girl, and was acting in ways that were very much different from what i expected from him. He felt no remorse for having toyed with another persons life, and having abused them and preyed on their insecurities he was very much aware of. I do not care much what has happened to him since graduation. Hopefully he learnt a lesson and changed his ways, but I cannot be sure.