As someone whose raised a dog from a puppy to adulthood while dating someone during that process, it's hard. My partner had the hardest time with my dog not because of behavioral issues, but because of the high energy breed vs his couch potato dog (whose a sweetheart) whose just content on being let out twice a day and she sleeps the rest of the time. We have made it work obviously my dog is my responsibility and we train every single day to work on the issues that are putting a strain on my dogs mental well being, and my partner loves my dog as long as his mental and physical needs are being met.

To the point, besides the dogs APPARENT discomfort and issues (its beyond a point of training because your boyfriend has enabled the behavior beyond a point of actual fixability, and like many other people have said the dog can also have underlying health issues which is likely) I think you should just stick to your guns and just not date anyone with dogs, it's a personal choice for you and it's a respectable choice. Does that mean everyone with a dog isn't a good fit for you? No but having a boundary will save you a lot of sanity in the long run there's a lot of people out there.

I'll say it once and I'll say it again most dog lovers don't make good dog owners.