My fiancée’s dog is driving me to my wits’ end and I don’t know what to do, any advice?

(This is kind of a rant, so sorry in advance)

I’ve been living with my fiancée for about four months now, since we got engaged. I love her, our relationship is great, and honestly everything is pretty much perfect, except for one thing. She has a six year old dachshund, and I’m at my limit with this dog.

He barks at literally everything, all the time, even at night, so I don’t always sleep well. If he doesn’t sleep in the bedroom with us, he cries all night and scratches at the door. The house is constantly dirty. If we leave, he cries for hours, and we basically can’t leave him alone for more than two or three hours or he’ll scratch walls or destroy stuff. He doesn’t listen to commands unless I raise my voice, and I hate having to do that. We hired a trainer, and while it helped somewhat, the behavior is still exhausting and honestly unbearable for me.

I didn’t think the dog would be this big of an issue when we moved in together, but I’m starting to lose my mind and I don’t know what the right move is anymore. Have you experienced something similar? Any advice or perspective would be appreciated.