Is it permissible to withdraw from a vow to fast in order to obtain a specific marriage, if the desire for this marriage ceases or its realization becomes impossible?

If a woman vows to fast until her marriage to a specific person materializes, then changes her mind or learns that he does not wish to marry, she must offer expiation for breaking an oath, because a vow is like an oath. The proof for this is the Prophet's (peace and blessings be upon him) saying: "The expiation for a vow is the expiation for an oath." And his saying when a woman asked him about her sister who had vowed to perform Hajj on foot: "Indeed, Allah gains nothing from your sister's hardship. Let her go riding and offer expiation for her oath."

The expiation for an oath is: feeding ten poor persons from the average food you feed your own families, or clothing them, or freeing a slave. Whoever cannot find the means should fast for three days, based on His (the Almighty's) saying: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten poor persons from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But he who finds not [the means to do so] - then a fast of three days. That is the expiation for your oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful."