Q: Does a person have only one Beshert or are there various possibilities and he/she needs to decide who is the right partner?
A: There is one person chosen by Heaven as it says in the Gemara in Sotah (2a) that forty days before one is born, a Divine voice says that the daughter of this person is to be marry to that person. How do we know - after all we do not have prophets? If we act properly, we will have Divine direction, i.e. we choose a spouse first based on intellect and then emotion. There are occasions that one's partner is not here because he was killed in a war or died for another reason but it is still possible to marry. This is what is called: "G-d makes the lonely ones dwell in a house" (Tehillim 68:7 according to Sotah ibid.), i.e. Hashem places the lonely who are not exactly matched into one house and they are a good match in the end. It is possible that it is difficult at first – "It is as difficult to find a match as it was to split the Red Sea (Sotah ibid.) – but they will work it out and live in love, fraternity and friendship. There is therefore no difference in actuality whether one marries his beshert or not. Either way, you must marry with respect and love and then invest energy.