Why not just find someone who is already content living their life single but enjoys the added social aspects of a relationship? That plus someone where those social aspects happen naturally without a lot of using the finite motivational energy.
Then there's no expectation or perceived responsibility to have a sort of dependency relationship, and the happy social reinforcing moments happen naturally.
The two ideas aren't mutually exclusive. Even happy and independent people have ups and downs, and can benefit from someone enthusiastically helping them promote their happiness.
It is a win win win for everyone involved.
The recipient of support is even happier, the supporter gets to enjoy the process of making the other happy, and then the supporter get the company of a very happy person.
Ideally this is bidirectional with each partner playing both roles.
It doesn't use finite motivational energy. It creates net positive energy.