Taking your questions in turn - no, I wouldn't stay in an unhappy relationship with a H who treated me like paid help because he earns more, and disrespects me.
No, I wouldn't stay to avoid messing up my DD.
Like PP, I strongly believe that staying in a relationship like that, where children see their mother treated badly and disrespected is far worse than leaving. Children learn by modelling the behaviour of their parents in the first instance - what message is your DD getting about what a relationship is meant to be? She is likely to seek out a relationship like that, or put up with a relationship like that herself when she grows up - because it is her normal.
I think the media has a lot to answer for when it talks about "broken homes", "failed marriages" etc - all those negative words. I do not believe that getting divorced/splitting always damages children. I have 2 children, their dad and I divorced when they were 3 and 1. They are balanced, rounded people, they are not broken at all. Because we have both been better parents apart than we were together. Even if only 1 of us had been a better parent apart, they would still have been better off - because we weren't happy together, and they weren't seeing a healthy relationship. Your DD can still have a loving relationship with her dad - and that is his responsibility to nurture.
You aren't being over sensitive. Any change like this threatens our normality, our sense of comfort zone (even when the status quo isn't comfortable). It can be scary and uncertain. What is it that you are most nervous/scared about? If you can identify that, you can put plans in place to combat it.
Ask yourself what it will be like if you are still here in 5 years' time.