This image was lost some time after publication.

The Facebook Prom was prophetic, signaling farewells, graduation, and the ending of teenage ties. As his colleagues were preparing to dance the night away at the Metreon, CTO Adam D'Angelo, a high school buddy of CEO Mark Zuckerberg, was saying his farewells. BoomTown reports that D'Angelo, 23, is leaving the company because "his responsibilities no longer fit well with his skills and interests." Even as the company tries to recreate a high-school environment to keep its employees tightly knit, Zuckerberg's own social network is fraying.

Cofounder Chris Hughes left a while ago to work on Barack Obama's presidential campaign. Another cofounder, Dustin Moskovitz, has been rumored to be on the outs with Zuckerberg, though Moskovitz attributes any disputes to normal friction between founders. And now D'Angelo — though not a founder, one of the small group who helped Facebook relocate from Zuckerberg's dorm room to Palo Alto — is gone, too. He may be leaving for his own reasons, but his departure is a sign that the company is fitfully growing up.