I am in agreement with several others. Take a step back and focus on being with your kids. Whether or not a Sarah will remain sober, is unfortunately not at all something that is within your control.
You should want to be with one of these women because you love them, and want to take that next life step with them. Until you can sort out these feelings be a dad to your two children (yes, I know one is not your biological child), and to your baby on the way.