Oh!!!!! I have a ZILLION bits of advice!!
The #1 most important thing is that your boyfriend does not in any way feel anger towards the dog. My male GSD Buddy is deathly terrified of my hubby and we've had him for almost 3 years now! My hubby gets mad because Buddy will run away from him and/or grumble at him and my hubby will yell at him (Stupid of my hubby I know but he's not the smartest )
All that does is makes things worse and reconfirms Buddy's fear of him. We'll take a few steps forward, then my hubby will get mad, and we take a few steps back.. it's so heartbreaking.
If he would just be nice to him or even ignore him 100% things would get better.
We've had behaviorists over and they have given great advice to follow, but my hubby does not follow it for too long.
I would advise contacting behaviorists it will help a GREAT deal for your boyfriend to understand what he has to do, and how the dog reacts to his actions.
My Buddy, like your dog, will let everyone pet him, except my hubby. Even my father in law can play and pet Buddy, just not my hubby.
Also.. Don’t put a deadline on when the dog will come around, it will be too much pressure. (when I first got Buddy my hubby told me we had 6 months to get Buddy to like him.. then it was a year... then 2 years.. yeah.. he's still here but that doesn't mean the hubby likes it!! )
If you would like, e-mail me at [email protected], I have tons of other things I can tell you to try or not to do!