expanded egoism that is focused on alter ego, a significant other for whom you care as much or even more than for yourself.
Chekhov's Darling is a perfect example of alter–egoism: she gives herself up to her loved ones and lives solely by their interests and feelings. This is her way to cherish her own ego.
Alter–egoism is different from altruism. Altruism is indiscriminate selfless concern for the well-being of others, whereas alter–egoism is very selective: it is directed on alter–egos, i.e. the chosen ones, and thus retains certain qualities of egoism.