Sometimes a person will reincarnate in order to marry his soul-mate…
Sometimes a man will reincarnate in order to marry his soul-mate because he did not merit to do so the first time. Sometimes he may have already married his soul-mate, but he sinned and must return to rectify it, as was explained above. In this case he will come back alone, as Sabba of Mishpatim has written (Zohar 105b) on the verse, "If he came by himself…" (Ex. 21:3) Sometimes he has merits, and even though she does not need to reincarnate she returns with him. This is the secret of the verse, "…his wife will go out with him". (ibid.)
The last two possibilities are opposite of each other. Either he sinned alone and returns alone without his soul mate, or he may have merit and she will return with him even though she has no need to reincarnate on her own.
Sometimes, a man did not merit to marry his soul-mate the first time, but a wife comes along for him according to his deeds. Among the souls of all the women in the world, there are none as close to him as this woman, even though she is not his actual soul-mate. When he sins and reincarnates, he will do so with this woman, even though she does not need to reincarnate for herself, and even though she is not his actual soul-mate.
Furthermore, there are some roots of souls, men and their feminine soul-mates, who have fallen off into the kelipot. It is possible that the males will be able to leave the kelipot into this world, but their female consorts cannot go out at all until Mashiach comes.
We have already learned that the female aspect is more susceptible to negative forces than the male because "…Her feet go down to death".
Now they are sunk and given over into the authority of the female kelipa.
We have already learned beforehand that the feminine aspect of the kelipa is lower and more deeply in trouble. Thus, the female aspects of these souls are in the lowest of places, and they cannot get out.
I have forgotten if her name [i.e. the name of the female kelipa] is "Igrit" daughter of Machlat, or "Naamah" mother of Sheidim.
"Sheidim" is also the Hebrew word for "demons", and no doubt this fact is applicable here.
Indeed, all the female souls of the entire root of Hur, son of Miriam, cannot leave until Mashiach comes.
Miriam is the sister of Moses, our teacher. Hur appears in the Book of Exodus, Chapters 17 and 24. He was also the grandfather of Bezalel, who knew how to permutate the letters by which the world was created, and consequently was the chief artisan in the construction of the Tabernacle.
I believe that I heard from my teacher that Aaron the Priest did not marry his soul-mate, since he was close to the root of the soul of Chur son of Miriam, his sister.
[From Shaar HaGilgulim, Chapter Eight, Section 1]