Rabbits get anxious when they feel vibrations through the floor, in the wild rabbits thump to signal danger to their group mates. Some rabbits react strongly to the rumble of a bass in music, others to vibrations from construction etc. It may be that your BF’s voice is loud and deep enough to evoke a similar reaction. My bun Breintje shuns many of my male friends because they have a tendency of being too loud for him. Some men have just a bit too much power in their voice.
What I would advice is to de-sensitise your rabbit to your BF’s voice through excercises. This is one excercise you could use to de-sensitise him. It may take a couple of tries before your bun gets calmer, it’s difficult to battle an instinct.
Make your rabbit feel comfortable by lying down together, all 3 of you. This is the universal rabbit language for: there’s no threat. He’ll feel more secure if you’re all down on the floor with him, like a group of rabbits all relaxing together. Pet your rabbit and make sure that he’s relaxed. Then have a soft conversation, even if it’s just nonsense words. Humming may also work, because that creates the same vibrations. Let your BF increase his volume in very small steps, but don’t make him speak directly into Bodies face, buns have very sensitive hearing. If necessary, make your BF face the ceiling when he talks, so the noise doesn’t go directly into Bodies face. Reward your rabbit with treats and pettings. This way your rabbit will learn that the voice is not a threat, and he may come to associate it with pleasant things like safety in numbers and awesome group hugs.