It's all been said really.
From a behaviourists perspective - she will get more anxious, more fearful, she may start to snap in certain situations where she feels she can't run away, and potentially this may not be at him! Dogs can start to pre-empt peoples actions and make mistakes, jump to conclusions about what someone is likely to do, and react more strongly if its someone they are NOT deathly afraid of, than they would to the person who instilled that fear.
This is how you end up with dogs who the owners say 'would not DARE... growl at/bite... me'.... because they have successfully punished the dog in certain contexts to stop giving communications like growling, lip curling, air snapping etc.
They assume the dog is 'trained' and then the dog bites someone else over a misunderstanding, someone reaching past them for something is mistaken for reaching to hit or grab a treasured item etc... often a child or a visitor!
So staying put means you risk your dog making mistakes, building a bite history, or bolting in fear and hurting herself/others in the process.
For her good, and yours, get rid of him.
(And please don't call out a behaviourist or trainer until you have left, because it is the absolute fucking pits being sat in someones house, telling a sneering bully how to handle/train their dog, knowing damn well they don't want to hear it, will do none of it and will likely use it against the dog and partner later on.)