Brighton-Le-Sands Beach. Great romantic style restaurants nearby to enjoy with your boyfriend, and to then enjoy an ice cream together on the beach. Perfect on a fairly windy and chilly Saturday night, in each others arms.
I would have to say the most beautiful and romantic place to go on a date would be Mona Vale beach on the Northern Beaches (for a day date). It is a really pretty beach (the type where a couple can meander for a while. After a walk or swim I love going to one of the cafés within walking distance from the beach. It is a romantic place to get a coffee.