A question I saw....?

I saw this question on another website, and was quite amazed that the answer was yes. The question was that " If a guy s in a women enough times and she doesn't get pregnant, that her body builds an immunity towards his sperm." The answer was yes. Is this true? The reason I ask is because me and my fiance have been together for 8 years and never use a condom (she has always been on Birth Control). If this is true can her body "eventually" go back to normal, and if we decide to have children later will she be able to have them?