Keep in mind that all this applies to friendships, but not romantic relationships. I've never used any of them though, so I can't tell you for sure how well they work. If that doesnt work, you might get the best answer if you post your question here. You can assign two Sims to have the exact same parents, and that should result in them being true siblings. There are several out there, depending on what "flavor" of slower or lack of decay you want. MasterController lets you change the relationship between the Sims, but you cannot set Sims to be siblings directly. For example, you can change the time of your game, pick the part of the day and set up the clock. While these are the main options of the Master Controller Mod, there are numerous other things that you can alter as well. To stop the decay by default though, you'd need a mod. Here you can also enable thetry for baby option for specific groups of Sims and disable it for others.
Those will decay even if the sims are merely romantic There is a cheat to change a relationship: testingcheatsenabled true, then go to the relationship panel and drag the bar to where you want it. Or they go to City Hall and take the Charisma class, and if it's a Sunday, they might find a dozen or so sims protesting who knows what outside in the street. My wannabe popular sims just camp out at the bookstore and can finish the challenge in an afternoon. Combine the two in one sim, and anyone they meet is an instant friend. (only one of them did which was a normal adult and was 1 of my starting 2) so after over a week in game I can see it isn't going to be fixed with time so I move them in and then out which seems to fix it however this causes one of my sims to disappear (the other one I.
#HOW TO STOP A RELATIONSHIP WITH MASTERCONTROLLER SIMS 3 FREE#
A sim who knows 25 others already achieves the Celebrity Charisma skill challenge and will automatically get a relationship bonus when meeting someone the same goes for a sim with the Attractive lifetime reward (15,000 points). So I had a teen sim and 6 adults (4 of them young adults) I get the free vacation event and most of my sims don't return. It's not even difficult to make so many friends either. I believe that a sim does need to learn the skill in order to get the benefit, but one point is enough. This is a bonus from finishing a challenge associated with the Charisma skill. If your sim makes 20 friends, those friendships will never decay on their own. The other way to keep friendships from decaying is through the game itself. There are several out there, depending on what "flavor" of slower or lack of decay you want. To stop the decay by default though, you'd need a mod.