I don't know if he was truly born again. Only he and God know that. We are human. We have free choice. Sometimes we make bad ones. Again, being born-again does not make one perfect (just redeemed and going to Heaven to be with Jesus Christ their Lord and Savior.)
His faith/thinking was apparently weak or had a moment of weakness. That's when satan slips in and temps. He uses money, power, sex, and fame. His faith didn't stop his free will. He chose to disobey. And now he has to answer to God.
Just so you know where you're Satan myth comes from:
http://en.wikipedia.org/wiki/Satan
The Hebrews refered to the Angles that prosecuted people going into heaven(oh I love saying it that way), "Satans". Literally - The Accusers. You're buddy Constantine chucked the verses/books that deal with this definition. The concept of Demons(like Azazel, Asmodeus) came from Zoroaster whom they were exposed to as slaves/exiles in Babylon. Basically you've got a 3000+ year bullshit story that's piggy-backed on another bullshit story that didn't scare people into submission back then either.