Is the rejection of the first suitor by a young woman after a long engagement and prior consent, and her subsequent association with another suitor who is geographically closer, with his knowledge of the previous engagement, considered a sin requiring repentance?

A young man proposing to you after learning of your acceptance of the first suitor is impermissible, due to the Prophet's (peace be upon him) saying: "A man should not propose over the proposal of his brother until he marries, or he leaves it." Your rejection of the first suitor for the sake of the second suitor is unlawful if the rejection was due to the second suitor. As for the marriage contract with the second suitor, it is valid according to the majority of scholars. It is obligatory for both of you to repent to Allah by ceasing the sin, regretting it, resolving not to return to it, and seeking forgiveness from the first suitor.