Can someone who has committed numerous sins and transgressions be considered a Muslim? And is his marriage to a foreign non-Muslim woman—after he had committed adultery with her and before he embraced Islam—considered illegitimate and grounds for divorce? What is the expiation for these sins? Can Allah forgive them? And will he be punished for them in this world?

Your committing of major sins like fornication (zina) and drinking alcohol, as long as you do not deem them permissible, does not expel you from Islam. However, repentance from them is obligatory. If the woman is not from the People of the Book, or if you married her before her repentance from fornication, then your marriage to her is invalid. Marriage to a non-Muslim woman is not permissible unless she is a chaste woman from the People of the Book. For the marriage to be maintained, a new contract is required. The children from this marriage are attributed to your lineage. Repentance is achieved by abandoning the sin, regretting it, and resolving not to return to it. Repentance is accepted and erases sins. Ibn Taymiyyah said: "The repentant person is not punished, neither in this world nor in the Hereafter, neither by divine law nor by divine decree."