Characters
Whoever said that plenty of fish in the sea thing was lying; sometimes there’s only one fish. Trust me.
— Ally • Ally McBeal

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker rejects the comforting saying that there are plenty of fish in the sea. Sometimes, they insist, only one will do, and no crowd of alternatives makes up for it. The plea to trust them gives the complaint a rueful, hard-won ring.
Context reviewed