Good relationships require clear communication and some semblance of equality.
If you're serious about staying with her, then you need to balance your needs against hers. It's a perfectly valid thing to say "I hate my job. I'm looking for one I enjoy more that pays less. If that happens, I won't be able to pay for your horse. If you want to keep your horse, we need to find a way to balance the budget."
Either she cares about you and has never developed financial muscles, in which case you two can get through with some hard decisions and be happier.
Or she doesn't care about you, and you should split.
I can be. She complains about our current 1800sf house being too small.