Why are men expected to keep a romantic relationship together with women?

I've seen a lot of videos on social media of women divorcing men, and after the divorce, she sad that he didn't fight to keep their romantic relationship alive. I believe that it shouldn't be just on the man to keep the relationship alive. Women should also show interest in keeping the relationship alive as well. Why do women expect men to keep the relationship alive? Is it because of his gender? What's y'alls opinion?
Why are men expected to keep a romantic relationship together with women?
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