Requires XML Injector

Also Recommended: Less Relationship Culling

This mod includes tweaks to existing neighborhood stories and new story arcs for sims to get engaged, get married, and split or merge households.

Tweaks

I made a lot of small tweaks to most of the existing neighborhood stories. This is not an exhaustive list, just the most notable changes.

Only sims in the same age category will start dating through neighborhood stories.
Neighborhood stories will take gender preference into account when selecting which sims start dating.
Sims who start dating through neighborhood stories will gain some friendship as well as romance.
Sims who become friends or start dating through neighborhood stories will be given the has-met relationship bit so they won't have to introduce themselves despite already having a relationship.
Sims who break up through neighborhood stories will actually have the proper relationship changes to make them break up.
Neighborhood stories breakups are a bit more likely, but the sims must have a low romance or friendship relationship score. Noncommittal sims and teens may also break up without having low relationship.
Sims can only become best friends through neighborhood stories if they are not already best friends.
Children can become friends or best friends with other children through neighborhood stories. This was previously only allowed for teens and older.
When relatives gain or lose friendship through neighborhood stories there is a chance that their family dynamic will change (requires Growing Together).
If the romance changes rule is allowed, sims in a romantic relationship can gain or lose romance, similar to the friendship stories. Their romance dynamic may change. (Note: I don't own Lovestruck, so I just used the same method as the family dynamics. It should work exactly the same, but let me know if there are any issues with this).
Changed the becoming despised story to declaring an enemy since despised is just a label based on relationship score. This also means that the same two sims can't have the story repeatedly.
Sims who call you asking if they should date someone may start dating exclusively if their date has gone well.

New Neighborhood Stories and Interactions

New household rules: Get Married, Individual Move In, Individual Move Out
Sims who are dating may get engaged if the romance changes rule is allowed.
Engaged sims may get married if the get married rule is allowed. They may also move in together and/or change their last names depending on other settings.
Sims who are in a romantic relationship may move in together if one household has the individual move in rule allowed and the other has the individual move out rule allowed.
Sims may move out into their own household if they have broken up but still live with their significant other.
Sims may move away from family members in their household. This will only be available for sims who are at least young adult age and have a parent, grandparent, sibling, or aunt/uncle in the household who is also young adult or older. They will take their significant others and children to a new household. They may also move into a house. This is more likely when they have children moving with them. Both the moving away from family and moving in stories will be discoverable at the mailbox and may appear in either order.
Sims may become companions with cats or dogs in their household if the friendship changes rule is allowed.
New interaction to suggest a sim to find a significant other. This is located under Relationship -> Other Sims, along with the Hook Up and Talk Up Sim interactions. This is not technically a neighborhood story, so it's not discoverable at a mailbox. It's essentially the same as the Hook Up interaction; you just don't specify which sim to date. They'll pick someone automatically or may call back to say that they couldn't find anyone.
New interactions to suggest sims get married or move in with their significant others, also located under Relationship -> Other Sims. These will trigger the marriage or moving neighborhood stories.
Interaction to have a sim update their last name to match their significant other. This is located in the actions menu. The sims will have their last names changed based on the settings you have chosen. This same interaction can also be done using the cheat console (ctrl+shift+c) by typing neighborhood_stories_expanded.update_last_names then both sims names. This cheat only takes the genders and name changing settings into account, not the sims' relationship status, so you could use this with any two sims.

Settings: This mod has a config file with settings. Shift+click on the mailbox to find the picker interaction to change them.

Blocking Traits

With the interactions in the actions menu, individual sims can be blocked from moving out of the household, getting married, or having romance changes. The rest of the household can have neighborhood stories based on the household rules, but a sim with blocking traits will not be selected for stories.

NPC Weddings Connection

If you also have my NPC Weddings and Invites mod, sims who get married when calling to ask if they should elope or when you choose not to attend the wedding but have them marry anyway will have their last names changed based on your chosen settings.

Rules to Decide Which Sims Move

Household moving rules will be used first. If one household has the move in rule allowed and the other has move out allowed, they are eligible to move. If the move is only allowed in one direction, the other direction will not be tried unless it's a marriage move and the ignore_moving_rules_for_marriage setting is True.
If the move is only allowed in one direction and the allow_move_to_homeless setting is False, we'll check that the move is not from a household with a home lot to one without. If it is, no move will happen; otherwise, the move will be attempted.
If the move is allowed in either direction, we need to decide which direction to try first.
If one household has a home lot and the other doesn't, we'll try to move to the lot first. If the allow_move_to_homeless setting is False, the other direction will be disallowed.
If both or neither of the households have a home lot, we'll check how many extra sims there are other than the moving partner and their dependents. The move to the household with fewer other sims will be tried first. If they have the same amount, we'll check how many dependents would be required to move. The direction that moves the fewest sims will be tried first.
Now the first direction to try has been selected. If the moving partner is the only adult in their household, the entire household must stay together. If there are other adults, only children of the moving sim who do not have another parent in the household are required to be moved. If the household being moved to can fit all of the sims required to move, the move will happen. If not, the other direction will need to be tried. If it's disallowed or also can't fit all the sims, no move will happen.
Once the required sims have been moved, if there is still room in the household more sims may be moved. If the move is from a household without a home lot to one with a home lot, children of the moving partner who were not required to move will move if the household has room for all of them. If there is still room, pets who are companions of the moving partner may be moved. Then companion pets of the other moved sims may be moved.

Important Note

One of the biggest issues with the current state of neighborhood stories is relationship culling. Any relationships between sims in the "Other Households" section of manage worlds get deleted almost immediately. Because of this you may get notifications about sims starting to date or becoming friends when checking the mailbox for neighborhood stories, but if you actually go into their households they haven't met. I recommend using my Less Relationship Culling mod to prevent this. You may also use a mod like MC Command Center to completely disable relationship culling. (MCCC Settings -> Relationship Settings -> Relationship Culling -> Bypass Relationship Culling). Some relationship culling is good for the game's performance, so you may not want to completely disable it, especially if you're noticing lag in your save. If you choose to leave the relationship culling unmodded, neighborhood stories engagements and marriages will be pretty rare since sims will not maintain the significant other relationship long enough to be eligible.

If you still have the file KaylaDot_NeighborhoodStoriesExpanded_RelationshipCullingPrevention.package, that is now replaced with the Less Relationship Culling mod and should be removed from your mods folder.

Neighborhood Stories Expanded