I know this issue occurs frequently in younger men, maybe it has to do with their libido or bravado. Though its common, every scenario is slightly different. It's embarrassing that I am asking this question when I am a dog trainer myself but when I explain I think this might be the job for a boyfriend trainer.
We have been living together for 6 months. We get along great, I love him dearly and can't imagine life without him. Before him I was married and I bought this chihuahua that is the most loyal and compassionate dog (to me) but that's how I like her. She is not mean to strangers, just is unsure, then almost always accepts them in due time.

My ex hub didn't like her for some reason, in the end I left him. Now this man is acting the same way! Physiologically tormenting her! She will puddle, shake, growl when he pretends to hurt me, even jumped in the shower with me when he came in the bathroom. I don't blame my dog! And there is no way I can train her to be a 100 ibs Sheppard that's 'badass'. Strangely there are tines he will take het for a walk hold her and try to play with her. This confuses me. The answer reading this of course sounds simple "pick the dog" don't worry people, my dog is not leaving, nor is my amazing soulmate that torments my dog. He tells me he does this because my dog growl and snaps when my daughter hits her And thinks I'm choosing the dog over her, completely untrue. I know my dog and know she has no history of biting. Anything is possible but my daughter is more likely to get hurt by tripping then my dog.

Then he will say he thinks he hates my dog because I bought her with my ex. Which is it dude! Either way I am stressed to tears, confused and this to end. I can't give away my dog, I don't want to leave the man I love but I can't have this anxiety and stress in my home! It's not healthy anyone! Btw, yes I have tried telling him how I feel on the matter, he said he will accept anything of mine except the dog.

So my novel will stop here, I would like someone to please give me advice to why this is happening to me?

I find this all strangely puzzling, starting with your premise that this is a common issue with younger men, what 'job' a 'boyfriend trainer' would do, why a trainer would allow a child to hit a dog, and why you assume that people will say 'pick the dog.'

Anyway, it really does sound very simple: he doesn't like your dog any more than your ex did, your dog is attached to you and perhaps you two are very protective of each other, and maybe you act more in love with your dog than you act with him, despite your feelings - we aren't there to see it. Why is this happening? Because it happens to lots of people, whether it's a dog or a child or the cap on the toothpaste.

Your options: leave him, wait for him to leave you, get couple counseling, or work on the couple counseling yourselves - sit down and work out a plan for getting along, based on COMPROMISE in order to stay together. Pretend there is a counselor sitting with you on the couch, and work it out in writing.

I have been having the same issue with my boyfriend. We rescued a min pin off the streets and he has come a long way but is very attached to me, sometimes my boyfriend will go to pet him and he will piddle or shake. He has refused to listen to him and this makes my boyfriend even more frustrated! So I got to thinking... I am always the one who feeds him, takes him out and trains him. Of course at this point being that Spanky will not even listen to him to go outside we have a problem. So I went to the pet store got some treats, they are only 1 calorie training treats. I bought 2 packs. One stays downstairs and the other up and only my boyfriend is allowed to give him those treats. This has improved their relationship 100 fold. I encourage him to say good boy and also offer affection gently and non constraining. It has only been 3 weeks and they are already bonding... sometimes I get jealous!! Lol but I never interact when they are having their special time and I never use those specific treats. Spanky has even started doing his basic commands with him. Give it a try!

I have friends that have a chihuahua and she is hell on four paws. She is the meanest thing. When we have parties over there, we ask if the "Little " will be upstairs. Give me a German Shepherd any day of the week.