One of the few live concerts I ever attended was CSN in Norman OK in ’77.
I am not enough of a fan to know all the details of Neil Young’s relationship with them, but he did sing some harmony here and there. They also did some extreme dabbling with Joni Mitchell (or was it night putting).
I think he had a liver transplant back in the 90s, from heavy drinking.
The band was legendary in the peace movement, and I believe played at Woodstock.
extexanwannabe 
Never was a fan.