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).
No, you can have SzPD and also a life partner. It can be as easy as getting married due to societal pressure, going with the flow of a relationship can often be significantly easier than fighting off questions about being a permanent single person. Relationships don't have to be lovely, loving things of deep attachment. They can also be points of stability, pooling resources, and taking advantage of societal carve-outs.
Must be a wonderful experience for the other person! Being someone’s point of stability for “societal carve-outs” instead of having your love and affection reciprocated.
I mean, the other person might also just need a point of stability and can otherwise get much of their social enrichment elsewhere. Your partner can just be a person you get along with that you live with like a good buddy that you might have sex with (if you enjoy sex). Your partner doesn't have to be your spiritual guru, your therapist, your life coach, your obsession, your reason to live, etc.
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.
I don't necessarily believe it would be impossible to reciprocate, but that there would be an atypical representation of love and needs disparate to what culture has inculcated (which itself leads to many misapprehensions).
Depending on the literature chosen, SzPDs can have "lively internal states" and be "exquisitely sensitive" it's just a question of expressing such things.
Context, I’m bipolar, not SzPD, so may not fully understand.
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.