Must a committed Muslim woman agree to marry a young man who has had previous relationships or commits sins, even if he claims to have repented?

You must adhere to the teachings of Islam, and your diligence in adhering to them is beloved to Allah. Your eagerness to choose a righteous husband is appreciated. A suitor known for his good character and religiosity should not be rejected because of a past he has repented from, for "one who repents from a sin is like one who has no sin." As for someone who has a criminal record and has not abandoned those past actions, his character and religiosity cannot be trusted. The suitor's statement that he has changed is not sufficient on its own. Choose the righteous man, even if he has a past but has repented from it, and reject one who has a past and has not abandoned it. The matter of a man choosing a religious woman applies equally to a woman choosing a man of religion and character, as stated in the Hadith (definition): "If someone whose religion and character you approve of comes to you [seeking marriage], then marry him. If you do not do so, there will be tribulation on earth and widespread corruption." What matters is the man's current state and his commitment to religion after his repentance.