Sims automatically perform certain romantic actions, even if they have a dislike for those actions. Because of this, relationship satisfaction drops very quickly.
Example: A Sim automatically flirts with their partner, even though both of them are dissatisfied with flirting. Relationship satisfaction drops, and as a result, the Sims start arguing.
Edit By Crinrict: Adjusted Title fit migrated bug report: [ARCHIVED] Sims excessively flirt with others | EA Forums - 11658323
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