This is actually the exact issue that I struggle with to really be able to invest the time into the product I'm working on. The spare time I have available to me, is actually better spent with my children.

I know some people may view that as a cop-out, that I am not really committing to my project, but I grew up with an absent father, and it's actually really important to me that while my kids are young, and looking to me and my wife for really key influence, I want to be there.

I figure that once they're young adults and want to go out drinking/partying, I'll have plenty of spare time, and I'll have wisely invested important time with my kids during that first ~15 years or so.

So right now, my project plods along - maybe 2 hours per week. I'd love to sink 20 hours a week into them. I tried working late nights, but you end up writing code that needs to be re-written, or coming up with marketing strategies/research that seems like you were smoking illicit substances at the time.

So in answer to the original question - a startup most definitely affects your relationship with your wife/girlfriend/family. Some of the structures other HN'ers have put in place sound like a good start.