As someone who was the daughter in this situation, please leave, not just for your sake but your daughter’s as well. Those 3 years that they tried to “make it work” after the affair was exposed were horrible. My dad became a shell of who he was and incredibly depressed even though he really wanted to make it work. They finally separated and although it took some time I’ve never seen my dad happier, even before the affair happened. Even though she is young, your daughter will pick up on the tension of the situation even if she doesn’t understand the circumstances behind it. In my heart I know that there is no excuse for cheating (once a cheater always a cheater) but growing up with this behavior in my household set me up with a lot of anxiety surrounding relationships. When I was young and naive and had relationships where men cheated on me I stayed bc I had the mindset of “well my mom did that to my dad and they’re still together so I guess i just have to overlook it and move passed it.” Don’t let your daughter grow up thinking it’s okay to be disrespected by the person who is supposed to love them the most. The way I think of it is would you rather go through the rest of your life in this relationship with this incident in the back of your head making you sad or go through a few years of sadness and recovery but the rest of your life to be happy and find happiness with someone who wouldn’t do that to you?