Relationships
Dating one person
Some systems prefer to all date one person, whether that's a partner system or a singlet that is their partner.
(A partner system is a system that another system sees as a partner collectively.)
When a system is collectively dating a singlet, not every alter has to be dating their partner. Every alter has different preferences, opinions and feelings, so this would make sense, especially in the case of littles (alters that are young children) because they are children.
When a system has a partner system, they may collectively feel as though they are in a romantic relationship, even if specific alters aren't dating. Others may consider a partner system as a system that has a lot of alters that are dating alters in their system. That's phrased poorly, so for better explanation, System A has a lot of alters that have partners in System B.
Dating multiple people
Sometimes, systems have multiple different partners, like all alters having their own separate partners, whether singlet or alter in another system. Some alters are even polyamorous, so they will have a polyamorous relationship with multiple people.
Alters can date people within their own system, alters within other systems, or singlets, but that's pretty obvious.
Innersystem dating
Alters can date other alters within their own system, since they are all their own people with their own opinions, feelings, etc. This is called innersystem dating. This is actually surprisingly normal, it's not much different than having family and friends within your own system!