A second suitor proposed to her after the first one; is she sinning if she accepts his proposal?
Question

A young man of good character proposed marriage to me, and I agreed, and we set a date for the engagement, but nothing was done officially. All that happened was that my brother gave him the answer, and his mother came to visit us. At the same time, another young man proposed marriage to me who is of better character than him, and I felt more comfortable with the new suitor. I felt more at ease with him than with the first one. If I agree to marry the second suitor, will I have committed any sin? Please note that I was not completely convinced about the first one.
Praise be to Allah.Before answering your question, we must first say something having to do with the second suitor: it is not permissible for anyone to propose to a woman to whom his brother [in faith] has already proposed.
It was narrated that Ibn ‘Umar (may Allah be pleased with him) said: The Prophet (blessings and peace of Allah be upon him) forbade outbidding [or undercutting] one another and forbade a man proposing to a woman to whom his brother [in faith] has already proposed, unless the suitor before him gives up the idea or gives him permission [to propose to her]. Narrated by al-Bukhari (4848) and Muslim (1412).
But if it so happens that more than one suitor proposes to a woman, because the second suitor, for example, was not aware of the first one, or for some other reason, then there is no blame on the woman for choosing the one who is best suited for her, even if he is the second one.
It is soundly narrated in the Sunnah that Mu‘awiyah and Abu Jahm both proposed to Fatimah bint Qays, and when she consulted the Prophet (blessings and peace of Allah be upon him), he advised her to marry a third man, namely Usamah ibn Zayd (may Allah be pleased with him).
Muslim (1480) narrated from Fatimah bint Qays (may Allah be pleased with her) that she came to the Messenger of Allah (blessings and peace of Allah be upon him) and told him: Mu‘awiyah ibn Abi Sufyan and Abu Jahm have both proposed to me. The Messenger of Allah (blessings and peace of Allah be upon him) said: “As for Abu Jahm, he is a man who beats women. As for Mu‘aawiyah, he is a poor man who has no wealth. Marry Usaamah ibn Zayd.”
So there is no blame on you for accepting the second one and rejecting the first one. The choice should be based on Islamic guidelines. In the answer to question no. 5202 , you will find a description of the ideal Muslim husband.
And Allah knows best.