Existence of le in a sentence

Bonjour Marsha!

The correct sentence will be- 

Tu révèles ton secret et nous révélons le nôtre.

Here, “le” is actually a part of the possessive pronoun- ‘le nôtre’ which means “ours”.

Also, le agrees in number and gender  to the object it refers to, that is, the secret in this case which is masculine singular.

Have a look at the following Kwiziq lesson->

Le nôtre/le vôtre/le leur/etc = Ours/yours/theirs (French Possessive Pronouns)

The sentence hence means-

You reveal your secret and we reveal ours.

Hope this helps!