Relationship issues are one thing, mental health is something else. They can get intertwined. You can contribute to the relationship issues and problem solving, but you can only have a suporting role in her mental health. She needs to do the work. The way she commented on you researching your dear dogs condition speaks volumes. It's on her to address her issues. How much has she done this? As someone with anxiety, I have to say this isn't something my husband can do for me. But it took me years to see how I can address it.

I'm all for fixing things, but you are not selfish for leaving your relationship. There are problems beyond your control. It is selfish of her to think you should compromise from the beginning. Invested or not, don't throw good time after bad.