Don't think author is replacing unhappy personal life with workaholism. He's saying that when you have low energy in some parts of your life, it drains into other parts.

Now that he enjoys his work more, he's finding that he also has more energy for gym / social situations etc.

I had the same experience in big tech. Lack of work progress made me depressed and bled into other parts of my life.

Startups have their own issues, but at least there's more momentum on most days. Important to go with well-funded ones in this environment though, preferably by the top VCs: https://topstartups.io/