So I deleted something that I thought was a mod I had... But it sadly wasn't. It was a part of the main game... how do i fix this besides reinstalling the game?

Have steam reverify your files - whatever's missing should get replaced.

it wont work it says one is missing and that itll download it but it never does

It always says that, for some unknown reason. My game is running perfectly fine - but if I ask steam to verify, I get that same message.... Once you've done the verify, including that bollixed message, have you tried the game again?

Yes, its still missing

Well, then, I think you're stuck with a reinstall.

What is it that you deleted?

it was called

Jehanna.esp

That's not part of the original game. It's a mod. That's why verifying your install doesn't reacquire it.

I deleted it from the "options" section on the launcher it was and the mod it would have been i just re downloaded and its still not working

What's not working? Can you be more specific about the actual issue you're encountering?