I Love You Alice B. Toklas!
(1968)

Harold (Peter Sellers) leaves his fiance Joyce (Joyce Van Patten) at the altar, having come to be fascinated by the hippie lifestyle Nancy (Leigh Taylor-Young) and his own brother embody. He embraces this new life with Nancy completely, but finds he can't have a committed relationship - hardly even a moment alone - with her. In fact, he hallucinates all the people from his old life amongst the revelers at a party Nancy's friends have started in his apartment, realizing that he only traded one kind of status-seeking for another.

For a time, he reverts back to his old life to the point that he once more is at the altar with Joyce. But again, he leaves her there, realizing that he doesn't know *what* he's now running out into the world looking for, but whatever it may be, it's "something beautiful" that will bring him true happiness.

Thanks Rori!
http://www.petersellersappreciationsociety.com