[Tired of Taxes]

That is absolutely correct. The mere fact that adultery has occurred is not evidence of nullity. Is this controversial?

I'm Catholic myself, but I don't understand why that is the Church's position.

[Arthur McGowan]

A declaration of nullity is a declaration that a marriage never existed.

The "breakdown" of a marriage is not, in itself, evidence that a marriage never existed. (People don't seem to be aware that all priests are instructed NEVER to discuss annulment [except academically, as in a class] unless it's a question of a marriage which has irrevocably broken down and has already resulted in civil divorce. If the breakdown of a marriage were ipso facto proof of nullity, there would be no annulment process at all.)

The only way to understand why the Church teaches what it does is to start with the definition of marriage. This, of course, the world is not interested in. The last thing anybody wants to hear in connection with Catholicism is a definition of terms.

The best possible resources for the layman (I use the term in the sense that would include clerics who are not canon lawyers) are two books by Dr. Edward Peters.

http://ascensionpress.com/products/annulments-and-the-catholic-church

http://www.abebooks.com/book-search/title/100-answers-to-your-questions-on-annulments/