This mod changes the short-term and long-term relationship decay. It does not affect the relationship points gained and lost from direct socials, all it affects is how the game decays relationships. Maxis made making friends and keeping them very easy in this game. The Lifetime Wants such as "Make 20 Best Friends" and so on are some of the easiest. All you need to do is find a Sim and keep pressing "Chat" over and over again until STR is 100, and then you can forget about that sim. After around 5 days, you'll see that your LTR with that sim is above 50, now all you need to do is give them a call and all of a sudden you are Best Friends.

I wanted to tune the values so that I would need to interact with them on a regular basis if I wanted to make and keep friends. You will not be able to just wait until the LTR is above 50 in like 4-5 days, because now STR decays faster than LTR increases. If you were to get your STR to 100 with a sim and your LTR is 0, then in 5 days, your STR will decay to 85, but your LTR will be at a mere 10, which will force you to actually socialize with that sim if you want to make friends. If you read the explanation below, it will be much more obvious what this mod does.

This is how Maxis made the relationship gain and decay, and how this mod changes it:

Sim-to-Sim

Maxis Sim-to-Sim STR:
If STR is higher than 0, it decays by -2 (-1 if BFFs). If STR is below 0, it increases by +2 (+3 if BFFs). The change happens every day at 16:00. The decay/increase stops at 0.
This mod Sim-to-Sim STR:
If STR is higher than 0, it decays by -3 (-1 if BFFs). If STR is below 0, it increases by +1 (+3 if BFFs). The change happens every day at 16:00. The decay/increase stops at 0.

Maxis Sim-to-Sim LTR:
If STR is higher than LTR, LTR increases by +3. If STR is lower than LTR, LTR decreases by -3. The change happens every 8 hours. LTR always tries to catch STR.
This mod Sim-to-Sim LTR:
If STR is higher than LTR, LTR increases by +1. If STR is lower than LTR, LTR decreases by -1. The change happens every 12 hours. LTR always tries to catch STR.

Sim-to-Pet/Pet-to-Pet

Maxis Sim-to-Pet/Pet-to-Pet STR:
If STR is higher than 0, it decays by -3 (-2 if wolf, 0 if Master/Mine/Pack). If STR is below 0 (25 if Master, 15 if Mine), it increases by +3 (+2 if wolf, +5 if Master, +4 if Mine, +3 if Pack). The change happens every day at 16:00. The decay/increase stops at 0 unless Master (stops at 25) or Mine (stops at 15).
This mod Sim-to-Pet/Pet-to-Pet STR:
If STR is higher than 0, it decays by -3 (-2 if wolf, 0 if Master/Mine/Pack). If STR is below 0 (25 if Master, 15 if Mine), it increases by +1 (+1 if wolf, +5 if Master, +4 if Mine, +3 if Pack). The change happens every day at 16:00. The decay/increase stops at 0 unless Master (stops at 25) or Mine (stops at 15).

Maxis Sim-to-Pet/Pet-to-Pet LTR:
If STR is higher than LTR, LTR increases by +3. If STR is lower than LTR, LTR decreases by -3. The change happens every 3 hours. LTR always tries to catch STR.
This mod Sim-to-Pet/Pet-to-Pet LTR:
If STR is higher than LTR, LTR increases by +1. If STR is lower than LTR, LTR decreases by -1. The change happens every 8 hours. LTR always tries to catch STR.

You can tune the values yourself. Open this package in Sim Package Editor. There should be 2 entries:
Tuning - STR Decay: This controls how much STR decays/increases every day. The bottom two values 0x14 and 0x15 do not have any labels, but they refer to how much STR decays/increases if sims are BFFs.
Tuning - Normalization: This controls how much and at what rate LTR changes.

In order to unrar this mod, you need the latest version of 7zip or WinRar.

This global mod modifies two resources in the objects.package file. Any other mod that modifies these resources will conflict with this mod:
Tuning - STR Decay/BCON/Group:0x7FF41B0C/Instance:0x00001001
Tuning - Normalization/BCON/Group:0x7FF41B0C/Instance:0x00001000