How do I stop my dog from barking at my boyfriend?

Hey Natalie let me see if I can answer your question.   I have had dogs all my life and our current puppy Santino has a very similar situation as your little guy.   He is afraid of Antonio sometimes but we found a way to fix it! As you know dogs can sometimes feel very threatened when they're approached by someone, something or some action they are not comfortable with.  This usually happens because of a bad experience when they were very young (between 0-14 weeks old) or they were not introduced to things when they were young.  This inexperience causes dogs to react to certain triggers.   It could be a bike, a runner, a man with hat or even a weird sound.  The negative behavior they are showing is them saying "I am not comfortable". So what can you do? You can try various gizmo they have like training collars that create a high pitched sound once the dog growls or barks.   It is inaudible to the human ears but to the dog it sound like "BOOM".   This behavioral training will cause them to bark less but not change there inherent behavior.  They still will not be comfortable but won't bark...until you remove the collar. Annoying right? Personally I like the direct training method better to have them stop barking.  Here are a few tricks I've learned. Giver of Food Have you boyfriend be the one that feeds the dog.   The dog will begin to associate your boyfriend with the giver of food.   You dog will then go look for him at feeding times. This association should also be re-enforced during walk.  Have you boyfriend hold the treats but show it to the dog once you leave the house.   The dog will then automatically look up at your boyfriend constantly to get some of the goodies. As you walk and see items that historically have caused him fear (Runners, bike riders, men in hats) have your boyfriend give the dog a treat.   Don't worry about stuffing him like a turkey, just keep giving him treats. Personally it takes about 2-weeks for this method to really begin to penetrate the mind of a dog.

That Antonio.  You know what, he's not that bad of a guy.  He always gives me good food.  --- Santino the Dog

During this training routine make sure your boyfriend does things like walk into the room slowly.   Show himself to the dog but in a non-threatening way.   I tell Antonio to walk into the room sideways or crouch when he approaches Santino.  This gives the dog the feeling that this isn't a threatening situation and they can be calm. Try these techniques and in no time your puppy will begin to love your boyfriend as much as he loves you. Good Luck!