What should be done to treat it?
Source: I’m decades old, somewhere between SzPD and AvPD. Still officially undiagnosed and not treated for it, despite of years of psychiatrical treatment… I just get antidepressants and anti-generalized-fear drugs (dunno what is proper name) and I’m left alone (literally).
A diagnosis proper would require brain mapping. My theory is there is a missing piece of circuitry like a bridge in the reward network of the brain.
It's not like Schizoid people go around sneakily pretending to love people only to turn off once the relationship is secured. Like any healthy relationship, open communication is expected. A schizoid person can simply say, "hey, I can't have a Hallmark Movie marriage" and their partner can just accept that. Maybe the partner is schizoid too. Maybe the relationship is an open one. Maybe the capacity to meet a schizoid person where they are is, in fact, the deep emotional validation that they share with each other that is the bedrock to the partnership (the schizoid person is finally accepted and can let down their guard a little, the partner gets an insight into their schizoid lover that no one else ever sees and revels in the intimacy and beauty of it). There are an infinite number of ways to have two adults enter an emotionally healthy relationship even if one of them is neurodivergent.
Depending on the literature chosen, SzPDs can have "lively internal states" and be "exquisitely sensitive" it's just a question of expressing such things.
Relationships don’t need to be based on love. You could seek out someone who is looking for someone to share responsibilities with. Imagine them as a coworker or roommate.
If the relationship works well, you might want to formalize it to get the societal benefits marriage can provide.
Most people can’t imagine this working out because they don’t want or function well in that kind of relationship.