What is the ruling on a fiancée abandoning her fiancé after an eight-year engagement and his financial deterioration, and her engagement to another person despite her father's approval?

May Allah Almighty reward the questioner for their affliction, reminding them of His words: ﴿And We will surely test you with something of fear and hunger and a loss of wealth and lives and fruits, but give good tidings to the patient, who, when disaster strikes them, say, "Indeed we belong to Allah, and indeed to Him we will return." Those are the ones upon whom are blessings from their Lord and mercy. And it is those who are the [rightly] guided.﴾ [Al-Baqarah: 155-157], and the words of the Prophet, peace and blessings be upon him: "No calamity befalls a Muslim but Allah expiates some of his sins because of it, even if it is a thorn that pricks him."

Regarding the engagement: It is not permissible for anyone to propose after another has already proposed and the mature prospective bride or her guardian has agreed, as the Prophet, peace and blessings be upon him, said: "A man must not make a proposal of marriage when his brother has already made a proposal, unless the first suitor gives it up or gives him permission." However, if the other suitor proposes after the first engagement has been annulled, there is no harm, even though annulling an engagement without a legitimate Shariah reason is undesirable.

As for the study expenses provided to the girl, it appears that they fall under the ruling of a gift given to the fiancée.