LOL do you really think tall, good looking and $ is a strong attraction for a reasonably healthy and secure person looking for a long term partner? So if he had had these attributes you would have "understood" and not found yourself being all judgey about her past choice? You must have a fairly low opinion of her -or maybe women generally -you really think she would have fallen for those attributes to that extent if he also was not a good person?
I would not move in with her unless you see yourself as a future stepparent, you have respect and admiration for her as a person no matter what choices she made in the past, You're making it unique and layered. It's pretty simple- she got involved with a person who lacked character and integrity, she married him for the wrong reasons and they share a child. Nothing much to process- either you're ok with her past choices or you're not, either you're ok with her being a mother or you're not. I personally would not be - as a prospect for marriage -because I wanted to marry a never married man who didn't have children and wanted to marry me and start a family with me- that was my strong preference.
I stuck to that with rare exception - dated a single dad for a few months -child was born while we were dating -then quickly realized it wasn't for me- but I didn't date people where I was that troubled by their past choices that I looked down on them/was turned off etc.
I'm also concerned your feelings on this could affect your feelings about her child. Her child deserves an environment where the adults are in a healthy, stable relationship. And make choices in her best interests always.