From my understanding and experience, I think union is the point, but it’s not a guarantee. So sometimes we might go through the struggles of awakening and separation, but not do enough to actually reach union in this lifetime.
Some think twin flames are here to push humanity forward. Others… yeah, it’s just about that fantastic relationship. I don’t see how anyone could really know for certain either way.
This was a great write-up about the journey that you might be interested in: