What is the path to repentance from living with the paternal aunt's married husband's wife at passionate times, knowing that no adultery was committed with her?

What you did with your uncle's wife is a great atrocity. Adultery with a close relative's wife is a greater sin than adultery with a neighbor's wife. Islamic law has warned against being lenient regarding boundaries with a spouse's relatives. Therefore, you must offer sincere repentance by abandoning the sin, regretting it, resolving never to return to it, and cutting off your relationship with this woman. You should get married if you are not already married, or fast, and seek help from Allah. Be sure to associate with righteous people, attend gatherings of knowledge and remembrance, and stay away from bad company and societies of disobedience. You must conceal your sin and advise your uncle to return to his home and not abandon his wife.