Becky, that is so awesome. I don't have any experience with an "alert" dog but my dog Cosmo who I got from a shelter nearly 7 years ago is quite good at sensing when my blood sugar starts to get low. I notice his change in behavior even more since I got a dexcom cgm. It's interesting how incredibly intuitive dogs are.
I wish you the best with your dog and your boyfriend. For me if push came to shove, I'd give up my husband long before I'd give up Cosmo, and he is fully aware of it.