How do you justify breaking up Sims?

I have only ever broken up one couple that I recall out of all the games. My sims usually marry their first loves and die only ever being with them.
Except one, she was dating Akira Kibo. He's the jealous type and would occasionally lay into my sim for no reason other than he was paranoid. She wasn't doing anything. Then one night at the romance festival he just put himself about flirting with everyone. So I dumped in right in front of the tea stands. It was glorious!