Suggest that she stop snooping. Your friend or relative may have discovered an affair or confirmed her suspicions of one by looking through text messages (like Elin), emails or receipts. Though it can be tempting to chase down the paper trail, remind your friend that this ultimately won't lead to the resolution she wants. "A better use of your friend's time is to explore what's going on in the relationship that would make cheating a desirable option," Fulbright says.
Pre-empt a confrontation. In the anger of the moment, the other woman (OW) is a target for feelings of hurt and rage. And although the OW definitely has some responsibility for the situation, suggest to your friend that confronting her won't bring any sort of closure. If she has kids, remind her that they are the priority. "Remind her that the affair is a symptom of a problem in the relationship and/or with the individual," says Fulbright.
Don't let her compare herself to the OW. Infidelity makes women scrutinize themselves and it's easy to go down the rabbit hole here. When your friend starts saying things like, "He never loved me," or "She must be so much prettier than me," tell her that this is often not the case. People cheat for a variety of reasons, but rarely is it to find someone better looking. (After all, if it could happen to Elizabeth Hurley...)
Allow her to react in her own way. Is your sister ripping up wedding pictures? Is your mom cracking jokes while her world crumbles around her? There is no "right" way to deal. Short of hurting or endangering herself or someone else (i.e.; taking a nine-iron to his SUV—or his head), let her do what she needs to do.