I completely relate to your situation and am living it myself- I am also the technical cofounder at a promising seed stage company. While the magnitude of my co

I completely relate to your situation and am living it myself- I am also the technical cofounder at a promising seed stage company. While the magnitude of my commitments was far less than yours (girlfriend vs wife+kid), it was only when I failed at one (girlfriend broke up/moved out) that I really got perspective on the other one. I had an honest conversation with my cofounders about my work-life balance last month and am already seeing the positive benefits. I made a renewed commitment to myself, and my strictly limited 8 hours of work have started feeling much more productive. I hope this helped and wish all the best to you and your daughter.