the way you have to look at is
1) from you point of view – he attacked her and might have hurt her if you hadnt dragged them appart
2) from the dogs view – hes was asurting himself and wouldnt have actualy hurt her, that is how dogs sort thier positions out
i do know how you felt when he had pinned her as when i had my puppy stan had him pinned by the throught to the floor once but that was only because the pup hadnt learnt his place and was pestering stan.
im not a behaviourist or anything but bev will be able to help more