You sound overall like a reasonable and smart person. It also sounds like yoi have decided based on the data you already have that you 'need' to stick it out till your child is older. Maybe because you think or hope your wife will change, or you know she won't and want to have a semblance of a family with her anyway. Or you really are putting your kid first- but it doesn't actually sound like you are.

I think you need more data - what your options actually are for custody and divorce. Be sneaky and clever and WIN. Smart reasonable people can do these things, if it's about your kid, you will. If you haven't taken the unicorn you have for your wife out back and shot it yet, now might be the time. You think she would run with your kid. She allows bad treatment of her kid and her husband.