Having a fear of dogs is a type of stimulus-specific phobia. Some people develop a dog phobia after being frightened or bitten by a dog. Sometimes, the problem comes on for no clear reason.
There is treatment. Your friend will need to be willing to devote the time to it. But lets set that issue aside for the moment.
The good news is that your friend does not have to become a dog lover. He just has to be comfortable with your dog. (Im imagining your pet has a sweet, affectionate temperament.)
Dog phobia is treated the same way as other specific phobias. Examples are fear of open spaces (agoraphobia) and fear of heights (acrophobia).
The main treatment is a form of behavioral therapy called desensitization. It may also be called exposure therapy. Working with a therapist, people gradually expose themselves to what scares them until it no longer triggers fear. Sometimes a person with a phobia can do this on their own with support.
Lets run through steps that might work in your boyfriends case:
Step 1: Watch videos that feature dogs.
Step 2: Encounter real dogs from a distance. Examples: Look through the windows of a pet store. Watch dogs through the fence of an enclosed park.
Step 3: Spend time with dogs restrained on leashes. Your dog is a great candidate for this step.
Step 4: Spend time with a dog that is not on a leash. Again, your pet is the top candidate for that job.
Relaxation and breathing exercises might help ease anxiety along the way. No medicine has proven effective in controlling specific phobias. But an anti-anxiety drug may provide some temporary relief. That may be useful at crucial points of exposure therapy.