I used to be the same way, a few years ago I'm not really sure what happened (may have been equal parts noble and laziness), I just no longer wanted to be "that guy" that was working at all hours - even in a semi-joyful way, like the "but I love what I do".
Yeah, I love what I do, but there's no reason I have to be making love to it >~40 hours/week.
I was a little bit surprised at that point to realize that many employers (in my industry, anyway), are totally fine with me not working extra hours, as long as I'm productive and output plenty of work during the 40. (Of course I'm willing to step it up for special needs....sometimes).
Man was I happier after that point.
Plus, it FORCED me to address the fact that I didn't have enough other stuff in my life to begin with - and I became a bit happier learning how to include those things.