No your not a bad person you just made a mistake with a breed of dog that will show you where your flaws are if you screw up, somewhere along the line! Been there done that.
His pack member is most likely not in any sort of danger but as others have said he bears close watching.
And your friends,.. yeah my dogs don't know my friends have dogs! I never put my dogs at risk and never put anyone else's dog at risk. You put there dog in harm's way and she got hurt, apparently they knew no more than you but you'll be lucky if your friendship doesn't take a hit.
He has now demonstrated that he can't be trusted around other dogs! No more dog parks no more doggie intros...you've been warned!
So what you do now determines what kind of guardian you are and finding a qualified certified trainer would be a step in the right direction. And no Petco's, not gonna cut it here for finding help!