People who are strongly committed to their relationships do sometimes show interesting protective processes: they may pay less attention to attractive alternatives or perceive them as less attractive.
But this does not mean they become biologically incapable of experiencing attraction.
It helps to separate at least four very different things:
1. noticing that someone is attractive;
2. feeling sexual or romantic interest;
3. consciously deciding to develop that interest;
4. taking a concrete action.
There is a huge distance between the first step and the fourth.
That is why monogamy in real life is usually better understood as an agreement about behavioral boundaries, rather than a promise that “from today onward, my brain will never respond to another person.”
Different couples draw those boundaries differently. For one couple, flirting may already violate the agreement. Another may be comfortable with crushes and fantasies but not physical contact. A third may structure the relationship under a completely different model.
So a more realistic promise is not “I will never find anyone else attractive again,” but:
We understand what fidelity means in our relationship, and I choose to respect those agreements.
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