No doubt it was painful to watch like pulling teeth
Again, if he had volunteered the information then "redeeming feature." but he was still trying to harm and injure Michael, for the Donship

While knowing or not knowing about Questadt made no difference whatsoever to Michael's defense Good or Bad, Frankie's brother was already on his way but he thought he would indict Michael and send him to prison which may very well deliver him the goods, Don Fredo

Fredo's reveal of Questadt eventually, only confirmed in no uncertain terms how he was in deeper with Roth against his own brother