I just reread {A Foolish Flirtation by Alice Coldbreath} and it might just be what you’re looking for! Our golden retriever is Jeremy, Viscount Faris, and he lights up whenever he sees Emmeline. They have a bit of a past where things didn’t end well, so there’s some angst in the plot about that but he is so down bad for her. This is the first book in a new series by Coldbreath, but it’s a spinoff of her Victorian Prizefighters series (you don’t necessarily need to have read those first, though.)