Unsatisfied relationships

Why am I always having to repair my sims relationship? They have the best compatibility, all their attraction turn on’s/off’s are aligned. 
I am attempting my first long lifespan legacy and I’m on gen5 but I’ve had this through most of gen4 as well. It’s getting to the point that it’s not possible to have a romantic relationship. I’ve tried everything. I get their relationship repaired and then the next day they wake up and they are looking to break up again, for no reason.