Discuss as:

This Friday, May 8: The latest on Drew Peterson; plus, why people cheat

It's been more than a year and a half since Stacy Peterson vanished, and for nearly all of that time, her husband, Drew Peterson, has been the only suspect in her disappearance. Now, he's been indicted for murder. Not Stacy's, but that of Kathleen Savio, his third wife - found dead in her bathtub in 2004.

One man with two wives, both of whom told loved ones they were afraid of him... both now gone. We'll have the latest.

And also: It's the scandal that brought down presidential candidate John Edwards and Governor of New York Eliot Spitzer: Infidelity.

Infidelity breaks hearts and raises questions, ones that continue to perplex us. Why does someone cheat? Are the reasons different for men and women? Are cheaters born... or made? And can you affair-proof your marriage? 

Visit msnbc.com for Breaking News, World News, and News about the Economy

Turns out, new science is revealing that a lot what we think we know about adultery, is wrong. Hoda Kotb helps us put some myths about infidelity to bed.

See it all on a two-hour Dateline at 9 p.m. ET, 8 p.m. CT.