Facebook changed users' email addresses and forced them to use new emails ending with @facebook.com.
However, here are easy steps for reverting back your email address on Facebook.
1) Go to your profile
2) Click "Update Info"
3) Click the "Edit" button in Contact Info section
4) Edit box with original and @facebook.com email address will appear. Here, you can change who can see your e-mail address and which e-mail addresses they can see.
5) Click on the circle along from the @facebook.com address
6) Change setting to "hidden from timeline"
7) Click on circle next to other email address and choose "shown on timeline"
8) Click "Save" at the bottom of the edit box