The time that we dedicate to the things and people that we love/like, when it's enough?

The question is generic and for good reason.
Yesterday, semi-seriously, my gf asked me when we'll have a baby, I answered, seriously, that it's gonna be when I'll feel ready to share the daily time with someone as demanding as another family member growing up.
Now, between job time, hobbies time and girlfriend (gonna marry soon) time the time is already tight and because I'm self sufficient about happiness and kind of a loner I don't share really much time with her most of the days, and from this realisation from her side she broke into crying.
From that experience I understood that there might be need some adjustment on my side.
But on another side I'm puzzled of how other families deal with this, because though my life I've seen couples/married-people that had not really much interactions with each other on a daily basis and seemed fine with living like that.

So knowing this context, what's your experience about this phenomenon through your life time?