Is what happened considered a divorce or a ẓihār, and what are the rulings that apply to each of them, taking into consideration the questioner's circumstances?

Dealing with foreign women online is dangerous, and one must sincerely repent from it. The words you uttered, by making your wife unlawful to you, mean that her unlawfulness was conditioned upon your return to the reprehensible act, and since that condition has been met, the unlawfulness takes effect. The unlawfulness of one's wife depends on the husband's intention, and you know your intention best. The expiation for an oath (kaffarat al-yamin) and for 'zihar' (injurious assimilation of one's wife to an unmarriageable kin) are explained in previous fatwas. If only feeding is possible, it is permissible to give money to a trustworthy charitable organization. There is no need to inform your wife of what happened or of the return after divorce. You must be wary of reprehensible acts, occupy your time with beneficial things, and associate with righteous people.