Partying Is Such Sweet Sorrow• Public Theater gala performance of Romeo & Juliet. Delacorte Theater, nr. Central Park W. and 81st St., 6 p.m. Expected guests at tonight’s show (which stars Oscar Isaac and Lauren Ambrose) include Tony Kushner, Mike Nichols, Eric Bogosian, and a bajillion famous actors. In other words, the Romeo & Juliet cast are performing what may be the most famous roles in Western history to a private audience of the world’s most accomplished theater professionals. It’s like distributing loaves and fishes to Jesus.