How often do your sim marriages fail?

I like to make a big deal about going through the worlds and choosing a perfect partner for my sim, then planning their future for them before they've even met. That tends to make me really attached to my sims' spouses and their relationships, and it hurts me to break them up. I think I divorced a couple once in 7 generations of my legacy save, but it broke my heart. Usually if I want to throw some drama in there I kill one of the spouses, because for some reason I'd rather that happen than they get divorced. Plus divorce makes it hard to figure out what to do with the kids :/

I think breakups might be something I'll play with in the future, but as of now I can't bear it :,(