“Three is not balanced — there are always two or one,” we’re told in an exclusive trailer for “Petit Mal.” Written and directed by Ruth Caudeli, the Tribeca title focuses on three young women in a throuple. Anto (Ana María Otálora), Marti (Silvia Varón), and Lai (Caudeli) happily share a home, but the balance of their relationship is disrupted when Lai leaves for a work trip.

When Marti films Anto, the latter protests. “Stop recording. We’re not all three together.” Anto seems particularly stricken by Lai’s absence.

“Petit Mal” is semi-autobiographical. “I am in a polyamorous throuple. The three of us live happy together,” Caudeli said in a statement. “But