I couldn't call what they had a relationship, a romance or even a friendship.
Daniel ignores this, and it turns out that you can fight fate.
To cap it off, even when things are set right, one married couple has to be separated, because the wife has a destiny in her own time, two centuries in the future for the husband.
Every moment he appears in has somebody trying to find a way to prevent this, but they eventually find out that no, not even the gods can save him, his time has come.
The implication being even the Sisters were bound by some higher power they could not control.
.