Monogamy is an agreement to keep sex (and often romance) inside one pairing. It can be a living vow or a quiet default people never actually discuss until someone strays. The agreement is the thing, not the feeling of never noticing another face.

People break monogamy by accident of impulse and by long secret plans. The repair, if there is one, is about truth and rebuilt terms, not about pretending attraction to others never existed. Some couples renegotiate into openness. Some recommit with clearer rules. Some end.

Monogamy is not morally heavier than ethical nonmonogamy. It is a structure. It fits people who want the simplicity of one sexual household and who are willing to decline other offers.

Say the rules out loud even if they seem obvious. Obvious rules are the ones that surprise you in year seven.