What is the reason for a married woman repeatedly dreaming of someone she loved in her adolescence, and are these dreams from Satan or from Allah, and how can they be stopped?

A vision is only from Allah if it is righteous. As for an unrighteous vision, it is a dream from Satan. Righteousness is either in terms of the form of the vision or its interpretation. What the questioner sees are nothing but dreams from Satan, due to their unrighteousness and lack of uprightness. There is no betrayal of the husband in them, nor do they indicate a rejection of repentance. Seeking refuge in Allah from them and following the prophetic etiquette is sufficient.