By no means is marriage or family essential for a full and happy life.
That claim is broad brush, one size fits all, bullshit, devoid of nuance.
Marriage and family is a massive dice roll.

While marriage and family CAN be a source of great fulfillment in life, these relationships can also inject chaos into people's lives, often to the point of ruining the lives of those involved to varying degrees.

It's worth pointing out that Buddha left his wife and son.
Likewise, Christ told people to give up everything they have and follow him...same thing. He was saying you gotta give it all up including relationships, not just possessions or monetary wealth. You even have to give up the concept of "you".

The 50 year old in the post you shared is attached to certain things and that's why they are suffering. Keeping up with the Joneses is not giving up everything you have. It's chasing everything you don't have.

If the grass is always greener, the answer is to burn the picket fence.