Cohabitation
After spending a while in the world of Avaria and forming interesting new relationships with the people you meet there, you may decide that you'd like to establish some kind of formal living situation with one or more of them. Cohabitation allows you to create a relationship with another character or characters where you share lodgings or a closer relationship with them. Depending on the type of cohabitation, this will give you the ability to create plot notes for one another, give duplicate keys to roommates, or share rent payments.
Types of Cohabitation
There are two different ways to establish a close living situation with another character, one using the COHABIT command and the other using the ROOMMATE command. These convey different perks, and can be used together or separately.
Cohabitants
The COHABIT command establishes the existence of a relationship with another character, signifying that they are sharing their lives closely. Cohabiting characters might be spouses, close friends, traveling companions, or simply people who happen to be sharing lodgings together as roommates. The establishment of a cohabitation can provide useful information for staff to use in interactions, and allows cohabiting characters to send plot notes to one another. The idea behind this is that characters who live together or otherwise share their lives closely will tend to notice things about each other's circumstances and habits that other people would overlook or simply be totally unaware of.
Cohabiting characters do not necessarily need to be sharing a room together. They might live in the same area outdoors -- for instance, camping at a single site together, or sharing the same sheltered spot under a bridge. On the other hand, they might not actually live together at all, but simply spend enough time in one another's company and know one another so well that each of them is very much in tune with what goes on in the other's life -- as in the case of best friends or very close family. Conversely, cohabiting characters might not be very close at all, but instead may be sharing a space due to other circumstances -- they're roommates, not soulmates! In this case it's proximity alone that may make them very much aware of what is going on in each other's lives (even if they might prefer not to be).
In the end, cohabitation doesn't necessarily mean any one particular thing. It's just a roleplaying tool that exists to help you tell stories and to ICly convey interesting information to other characters with whom your own character is close.
Establishing Cohabitation
It's very simple to set up cohabitation with another character. While the two of you are in the same room of the game together, simply cohabit (with) <character>. This will give the other person a chance to either accept cohabitation (with) <character> or decline cohabitation (with) <character>. A cohabitation request doesn't even need to be acted upon right away -- the invitee has up to 3 days to consider it before the request expires.
If you no longer want to be considered someone's cohabitant, you can simply leave cohabitation/habitation at any time or place.
Additional Cohabitants
You can establish a cohabitant relationship with up to five other people, for a total of six members of a cohabitation group. This could be a bunch of family members, a close-knit group of friends, or just some people who happen to be sharing the same living arrangements. You could consider this an inner circle of sorts -- though potentially without the implied trust, depending on the exact relationship involved. In any case, if you are a cohabitant with one person, you are automatically considered to be cohabitants with that person's other cohabitants as well, even if you didn't accept a request made directly to you.
Creating Plot Notes
The biggest perk of being cohabitants is that you can create plot notes for one another! These are simply things about your character's present life and habits that you think someone else close to them (emotionally or just spatially) might pick up on. To send a plot note, all you have to do is send plot note (to) <character> <plot note text>, where the text is whatever you want it to be. Plot notes like these might include information like, "Donna never came home last night", or "Waraqa's sleepwalking is getting worse", or any of a number of other things.
In situations where you have more than one cohabitant, this means you have the option to create special notes for any of them, but plot notes created for one cohabitant are not automatically shared with the others as well. This allows you to tailor your notes specifically to each person based on what you think they would be most likely to notice. For instance, your really close cohabitant might realize you have suddenly renounced all your favorite foods and seem down, while another cohabitant who can't stand you only notices that you're no longer spitting pistachio shells all over the floor -- One True God be praised!
Roommates
If you want to simply establish that you're sharing lodgings with another person without necessarily implying any closeness at all, you can use the ROOMMATE command. This allows you to have duplicate keys for the same room and to share the costs of paying rent. You won't, however, be able to create plot notes for one another unless you also COHABIT. In many cases you may wish to do both! But the ROOMMATE command on its own is useful for situations where, for example, you're simply sharing a saferoom or club where you meet up but don't live, or you live together but have completely opposite schedules, or you live somewhere large enough that you might not be all that aware of what the other person is doing, or you're just allowing someone to live in a room you no longer use.
Adding and Removing Roommates
When you want to add a roommate to your lodgings, you can go to the lodging rental location with your prospective roommate and roommate add <person>. This will immediately grant them a separate key and potential rent-paying privileges (or burdens, depending on point of view). To remove your roommate, simply roommate remove <person>.
Additional Roommates
Just like cohabitants, you can have multiple roommates as well. Again, the default limit is a maximum of six people sharing a room. Each new prospective roommate must be added from the main rental area of your place of lodgings, where they will receive their own key. Only the original owner/renter of the lodging has the ability to add roommates.