Personally, I'd totally ignore the want to break up. Sims 4 AI is primitive and fairly ludicrous, IMO. If a Sim is in a committed relationship, they will always get the want to get out of it. If they're not, they will always get the want to enter into one. It doesn't matter if the relationship (or lack thereof) is good or bad, if it fits their personality or not -- they just always want the opposite thing. If they don't have a plumbing bee-box, they'll harass you with wants to buy one until the end of time, etc.
In a nutshell, always have them do what YOU want them to do.