How do you justify breaking up Sims?

What I like to do is play the other household and see what kind of dynamics is going on between the husband and wife. Then I decide from there if this is something I want to mess up, or not.

I play it that, while things were going smoothly, my sim was getting bored with the relationship and wanted to shake things up. Thought they could date someone else with more danger, spice, etc. So they call it off. Maybe they regret it later, after dating around and realizing they had something good, or maybe they regret it later. Maybe they try and get back together. Or, maybe they really do find someone else they click with better.

My sim started to date a sim whose a hot head, and they’ve been having a nice time together but he got a moodlet that made him angry so he stared to yell at his gf. I switched control to his household and decided to break up with her. I liked them both together but I’m looking at it like a new way for the two to turn over a new page. I’ve changed how they look and they adopted new hobbies and the guy got a new job. I might get them back together but only after she’s tried to date someone else.

I sometimes just do this for the giggles. Then again I can be cruel to sims.

Take them to the romance festival get the sim flirty and start chatting in a group. They'll most certainly start flirting around with other sims and there's your excuse!

Like in real life, sometimes people like each other and get along great but there's just no 'chemistry' there. I usually play it that way. My sims were great friends but discovered they really had no chemistry with each other and decided to just be friends.

Just friends seems to actually work in the Simiverse :) My male sim's best friend is his former lover, Paolo. Interestingly enough, Paolo even gets along great with my sims's new wife Estelle... Even if he (Paolo) does cast longing glances, from time to time, at Thomas.

I definitely play for the story as well. Most of the time I will have either of the couple have some sort of fling with another sim. I have MCCC so it's fun to play with the risky pregnancy. My last couple was both high power career people and their jobs became more important than their relationship. So slowly I just had them get into fights to slowly deteriorate their relationship. I wanted to play it out but the wife died of tainted wine (pufferfish bug). So I have him now raising his son as a single dad.

The biggest thing holding me back from breaking up couples is that damned moodlet.

Something else I've played around with is having one sim go through a big personal change of some kind -- new job that pulls them away, new friend who their partner doesn't like, or even the re-traiting potion to shake up who they are (which could be in addition to something else happening). Then even though they got along before, they just outgrew the relationship and that can shake things up enough to have the breakup a part of a whole story.

I don't really justify it because it's just a game and all's fair. For example, I know that it would be pretty easy to break up the Heckings because the preppy guy is chronically kind of snotty with his husband even though he has the Romantic trait. I haven't done it yet though.