I was asked today why I stay

And that's a very fair question. The friend who asked me is also having some issues so she wondered what my motivation to stay was.
I have 3 main reasons for staying.
The first is security. Right now I have nowhere else to go. At least nowhere permanent. I'm not moving in with either of my parents or either of my grandparents. If I have to for a little while it's not the end of the world, but if I'm leaving I will know that within a few weeks I will have somewhere permanent for my daughter and I to live. It's something I would have to research more before I left this house. We have a routine here and I'm not willing to mess with that for my daughter's sake until I have a permanent place for us to find a new routine.
The second is because of Quinn. Because growing up my dad was barely around and I don't want her to go through that if this is actually something that we work through. I know if I stay permanently it can't be because of her, it has to be because I want to stay. But for now it's a major factor in this.
The third and biggest reason is because I can't erase the fact that we've known each other since we were 14 and been best friends for most of that time. We've known each other for 11 years. And most of that 11 years in one way or another was leading up to us being together and starting a family. Now our family is very broken and I did not do the breaking, but I need to figure out if I'm willing to put forth the effort to fix it before I leave for sure. I need to be at least mostly sure that leaving is what I want before I follow through. I don't want to make a mistake of my own and find out later I could have forgiven him and regret leaving him.