For about three thousand years, give or take 500, our planet has been dominated by patriarchal systems. They flourished because one of the main components of patriarchy is Violence. Its favorite pastime is to dominate, subjugate, enslave, oppress, intimidate, bully, fear-monger, war-monger, and most of all, kill.
In order to keep women from fighting back, from regaining control over their destinies, there was an extremely slow but successful campaign of brainwashing that purposely pitted women against each other.
One of the biggest successes against women is to convince her that all other women are to be considered rivals. When a woman is in a relationship where straying is not allowed, and her mate–male or female makes no difference in the 21st century but for the purposes of science and historical context, I’m going with the hetero angle here–desires another woman, societal rules have brainwashed us into believing that “the other woman” is the enemy. Thought successfully deflects blame from the source of the betrayal: the betrayer.
It’s not Normal. It’s a trick, a blindfold, a subterfuge. We actively participate in our own deception. Why? How did this happen? That’s a long-winded explanation that I’ll just go ahead and delete.
Do yourselves a favor. The next time someone cheats on you, don’t blame the other woman (or man, because we *are* in the 21st century). They aren’t the ones who’ve broken your trust and betrayed you. Blaming someone other than your significant other is to lie to yourself about who takes blame. It might be him *and* you, or it might just be him. But believe me. It ain’t the other woman and it’s beneath you to lay the guilt at the feet of someone else, regardless of how well they’ve been an active participant.