Hi Ironbird,
That's a tough one to answer, since it's apples and oranges, really. Probably someone with untreated PTSD can have a relationship for decades- how healthy either partner would be is what would beg the question but that's truly an opinion. If one's PTSD manifests so that it does push people away, you've answered your own question, however.
We all needed some catalyst, I think, to go get help, be treated, stop suffering needlessly. Perhaps lonliness is the one which will be the deciding factor here. It is so much a kindness to oneself to reach out and do something about the cycle of unmanagable life finally, and so necessary. Everyone deserves the life the 'wish' they had, one where PTSD does not leave you alone, exhausted, in pain and shredded daily. Reaching out for help is the way to get there.
Do take care, ok?
Anni