Hank, it’s important to first ask yourself what you want to achieve with your affidavit as the final outcome.
I have seen a lot of parents seek a shared care arrangement for their children whilst at the same time doing their very best to assassinate the character of their ex-partner within their affidavit, despite the fact that that approach is almost always doomed to fail.
A good rule of thumb is to try and remain as objective as possible when compiling your affidavit and list the good qualities of your ex-wife as well as some of the behaviors that are now creating issues.
You should also remember that although certain events in your relationships history may be very significant to you, they may not necessarily be legally relevant and as such try to be brief and only refer to the information that a court will consider as being legally relevant.
Below are a few links that discuss how to write an affidavit.
The internet is quite literally littered with web-pages that both, detail how to write an affidavit and provide real world examples of previously used affidavits (just search Google images for family court affidavits).