Should I confront the third party in my spouse's relationship?

It is usually better to deal with your own spouse, because they are the one who pledged faithfulness to you, not the third party. Confronting the third party easily turns into a fight, slander, or a risk to your safety, and rarely resolves the real cause. First find out what really happened before acting: “investigate, to establish the truth” (Surah al-Hujurat 49:6). If you feel you must say something, do it in a short, polite written message, or through a mediator. Focus your energy on repairing the relationship with your spouse and deciding whether it can be saved. See counselling.