Is the wife considered forbidden to her husband after he said to her: "If such-and-such happens and you don't tell me, then when I return from my trip, you will be forbidden to me for life, and if I approach you, I will be in the right and you the fornicator," knowing that she subsequently took the initiative to tell him everything that happened?

The prohibition did not occur as long as the wife did not conceal (anything). You must repent to Allah for uttering the prohibition of your wife. Your statement to your wife, "If you come to her, you would be right, and she would be an adulteress," is a reprehensible and false statement; do not repeat anything like it. Avoid the causes of intense anger, for the Prophet, peace and blessings be upon him, advised: "Do not get angry."