EXCLUSIVE

Before Kanye West was nailin' Kim Kardashian ... he used to nail other chicks while watching Ray J nail Kim Kardashian.

Multiple sources with first-hand knowledge of the situation tell us ... Kanye used the Kim K sex tape in the bedroom to get him in the mood ... and it always worked.

As we previously reported, Kanye has had a thing for Kim dating back several years ... and even tried to get her to break up with Reggie Bush in 2009 so they could get together.

We know he loves the sex tape ... he even raps about it on his upcoming album.