1. “Unchastity” (부정행위) need not amount to actual sex. Romantic text message exchanges can suffice.
2. However, once you “forgive” or “had condoned” such acts, you can no longer invoke “unchastity” and file for divorce unilaterally. (It’s a clean slate.)
3. In Korea, secretly recording a conversation you are part of, is perfectly legal. Wiretapping is not. Wiretapping in order to obtain evidence your spouse is cheating on you is still a crime, but the court/jury might go easy on you.
May divorce be with you (w/o turning into a criminal)!