If your partner cheats on you, they are the party at fault, not the person they cheated with. Particularly, since many affairs are carried out without the other person knowing they are dallying with a partnered person.
However, there are certainly exceptions. There are those who actively pursue flings with people with spouses, fiances or serious (monogamous) partners, with no empathy or care extended towards the relationship they are wrecking.
If your relationship was torn apart by a partner who cheated with someone who knew you, or knew of you, it's only natural to at some point fantasize about revenge. But when push comes to shove, many of the most obvious forms of revenge will hurt you more than them.
"WIBTA if I don’t hire a fully qualified girl for a job because she is the one who cheated with my fiancé? (Cheating was almost 4 years ago).