What should I do regarding a Muslim woman I proposed to with the intention of marriage, and then discovered she is still in the process of divorcing her husband, even though she affirmed that she does not want to return to him?

It is impermissible to propose to a married woman or to approach her, and it is not lawful to marry her, based on the Almighty's saying: "And [also forbidden are] all married women," meaning those who have husbands. And whoever marries her, knowing it is forbidden, is an adulterer. Communication with her must be severed because she is a non-mahram, and it is not permissible to communicate with her with the intention of marriage while she is still married to her husband; otherwise, this would be considered incitement.