How do you get your sim to leave another sim at the altar on sims 2?

While engaged, do interactions that bring the relationship down, i say about 50 or 40 or 30, something like that. Then click the wedding altar anytime you like, and if the relationship is 50 and down, one of the sims will leave the altar, fleeing. This happens to me alot, and let me tell you. . .it's embarassing, heartbreaking and funny all at the same time.

have a good day! ;)