Why table has drop, but the foreign key still there?

Here are the simple things I did

create table state (
state_code      char(2) not null,
state           varchar(15) not null,
primary key (state_code)
);

create table whitepage (
user_id char(8) not null,
email   varchar(50),
telephone       char(16) not null,
contact_name    varchar(30) not null,
city    varchar(20),
state_code      char(2),
primary key (user_id),
foreign key (state_code) references state (state_code)
);


insert into state (state_code,state) values ('GU','Guam');
drop table whitepage;
delete from state where state_code = 'GU';
ERROR:   Relation "whitepage" does not exist

Why I got this error message??!!
The whitepage table already drop. When the table drop, will the
foreign key constraint also drop??

Now, order for me delete a row from state table, I HAVE TO
re-create whitepage table. That's silly!!!

What shall I do? How do I delete a row in state without
re-create the whitepage table???

Thank you very much in advance!