She swore to her fiancé that she would never leave him, then she called off the engagement

Firstly:

She swore that she would not call off the engagement then she broke it off

If you swore by Allah that you would not leave your fiancé unless he left you, and you left him before he left you, in that case you have broken your oath and you must offer expiation for breaking your oath (kafaarat yameen). Expiation for breaking an oath is: freeing a slave, or feeding ten poor persons, or clothing them. Whoever is not able to do that must fast for three days, because Allah, may He be glorified, says (interpretation of the meaning):

“Allah will not impose blame upon you for what is meaningless in your oaths, but He will impose blame upon you for [breaking] what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] – then a fast of three days [is required]. That is the expiation for oaths when you have sworn. But guard your oaths” [al-Maa’idah 5:89].

It is acceptable to give each poor person a meal, or one and a half kilograms of rice.

Secondly:

Is it permissible to call off an engagement?

There is no blame on a person, man or woman, for calling off an engagement, because engagement is a non-binding promise. However, it is disliked (makrooh) to call it off for no reason.

Ibn Qudaamah (may Allah have mercy on him) said: It is not makrooh (disliked) for her to change her mind if she decides that she does not like the suitor, because marriage is a contract that will last a lifetime, so she has the right to be prudent and err on the side of caution.

If they decide to call it off for no reason, however, that is makrooh because it is breaking a promise and going back on one’s word, but it is not haraam, because there is no binding commitment. That is like one who offers a product for a price, then decides that he does not want to sell it.

End quote from al-Mughni (7/146).

Shaykh Ibn Baaz (may Allah have mercy on him) was asked: What is the Islamic ruling in your view, O shaykh, regarding a young man who proposed to a young woman, and the engagement continued for approximately two years, but the young man drifted away from her for family reasons – what is the ruling on that?

He replied: There is nothing wrong with that, if he proposed then decided not to go ahead with marriage. There is nothing wrong with that, whether that happened after one year, or less than that or longer than that, if he proposed to her then decided not to marry her, or she agreed then recanted. There is no blame, praise be to Allah. So long as the marriage contract was not done, each of them has the option to cancel.

End quote from Fatawa Noor ‘ala ad-Darb (20/148).

So you are not obliged to continue the engagement, and you are not obliged to go back to this suitor now, but you have to offer expiation for breaking your oath.

There is nothing wrong with placing one’s hand on the Mus-haf when swearing by Allah, and it is an affirmation of the oath, but it does not lead to any additional ruling. And it is permissible to swear by the Mus-haf itself – i.e., by the words of Allah, may He be exalted, because His words are one of His attributes.

For more information, please see the answer to question no. 203252.

We should point out about that the fiancé is still a non-mahram to his fiancée so it is not permissible for him to be alone with her or to touch her or look at her, except a look for the purpose of deciding whether to propose to her only.

And Allah knows best.