From Pluralpedia, the collaborative plurality dictionary
homesickness (n., v., adj.)
Applies tosystems, headmates

Homesickness is described as longing or yearning to go home. This can be experienced by systems who has at least one member who doesn't currently live in their home town, be it a layer, cosmos, or any location in the external world. This can also be felt by those who have been sourced from media that has depicted them being removed from it partway through a movie, TV series, book, video game, etc.

Homesickness can be caused by a member's hometown in their layer or cosmos of origin being lost due to system collapse or falling into disrepair, a factive who cannot live in the external world anymore, or a fictive being unable to live in their source due to being written out part-way through depending on the system's structure.

Boiled down to its simplest definition, a homesick member may or may not be able to return home. The severity of homesickness varies by how supportive their fellow members are, the ease of visiting their home or if they can return at all, and unique personality traits just to name a few factors. All system members of all roles are capable of feeling homesick no matter their system's and individual origins.

Sometimes, homesickness is caused by longing for a loved one, like a friend, partner, or their family.