My pup does not like any men either, except my Dad & sister's bf, but they've been in her life since day one. But you said this is all of a sudden so it makes me think something scared her & she associates it with him whether he's the source or not. It could be something as simple as a lough sneeze or opening a noisy shopping bag. They get spooked by the smallest things sometimes.
The other side of it, too, is unless you have been with your bf 100% of the time your dog was around it could be hard to say. I would be cautious & never leave them alone together. I'm not implying anything, but at the same time I don't think she would act this way for no reason. My advice is always the same: trust your gut, I don't think it will ever fail you.
Hopefully it's something minor & your bf having positive interactions with her over time will bring her back around.
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