What tv show/film is it when a man first says I love you to his Girlfriend when he thinks she's asleep?

He says I love You for the first time while he thinks she's asleep and
then I think she goes on to talk about it with all her friends whether
she should say it back, and i think, if i'm right, she actually says
it back to him while he's asleep?

For some reason im thinking Sex and the City but can't find anything
online. Any help?