Please use this thread going forward: Romantic Relationships decay/become negative fast with no interaction | EA Forums - 4947168
I've had this problem recently too, to the point my sims got DIVORCED! They also every few sims days would mutually develop a fear of being cheated on, despite neither having the jealous trait. I'd solve the fear and then the literal next day they'd develop it again. I had to disable fears to get that part to stop, but you can't disable relationship decay without mods. They'll go like, a single sim day, without doing romantic interactions and their once full love bar will be half empty. Infuriating.
I had forgotten that - yes, my sims are constantly getting fears related to their relationships regardless of how well the relationship is going or any of the statuses.
After a few in-game days (playing at normal speed) they seem to develop the fears and they seem to constantly have one fear or another, whether it is of being cheated on or being alone, despite interacting with their partner every day. I wouldn't say this is true for every sim, but it is for most.
At this point I am feeling like "Lovestruck" should be renamed "Never have fulfilling relationships".
Testing on my engaged Sims who live in different households today. I maxed their relationship again, they had a very successful date but their relationship immediately dropped again the next day, then really dropped the next day after that. I did this 3 times and tracked it.
From the Sim's profile (Image 1) it's clear I can't do anything more to make these Sims a stronger couple. They also have Likes/Turn ons matching each other. They were perfectly happy before Lovestruck.
Also their Attraction and Satisfaction keep becoming unknown. So as well as having to focus on constant Romantic Interactions with a Sim in another household, my Sims must also need to be constantly asking each other about their Attraction and Satisfaction. Which all sounds more that a bit needy. I'm sure it's not meant to work this way. Can you imagine having a couple constantly checking these IRL as well as needing to constantly flirt? Nobody would want to be friends with that couple.
Image 2 is the level it's dropped to from Max by afternoon when she stayed over and only left that morning. Image 3 is the level it's dropped to by the following night after not seeing each other and only having a flirty phonecall.
