Sorry for the somewhat harsh words. You have a point. The problem is that it’s way too easy to fall down the codependency rabbit hole when you start thinking of it as “I can’t do X unless someone else Y’s”. It was true for me, and I just wanted to make sure it wouldn’t be true for the poor fella going through marriage problems.

The trick and the trouble is that it’s easy to acknowledge the importance of being independent, especially in a romantic relationship, vs actually doing that in practice. After your 30’s your friends start to fade away, and one day I woke up without any except my wife. That was clearly a degenerate situation unfair to her, and expanding your social circle is something that should be done independent of whatever relationship you happen to be in. In fact, needs to be done.

Another complication / nuance is that, of course you should be serving and supporting your partner (and vice versa)! Its part of what makes relationships rewarding. They're not always 50/50 in all aspects.

The trick, as you say, is to know when that is crossing into something unfair. When it goes beyond something like who does the dishes or makes the most money into supporting the other person's core identity. Or when it becomes unsustainable / exhausting for other person. Identifying these issues can be difficult. It requires both partners to be in touch with their feelings and able to communicate openly.