"It will not be long before you get well"
I found this sentence from my grammar book and wonder why we don't say "It will not be long before you will get well"
*Not a teacher
It is correct.
It will not be long before you get well.
The highlighted clause is temporal (before introduces a temporal clause). We never use future tenses in temporal clauses. In order to express the future in temporal clauses we use present tenses.