Had something similar to this happen to me. I had a friend who now has a Master's degree in Philosophy. He seemed like a young believer but a believer nonetheless. I enjoyed discussing theology and philosophy with him and I began to notice a shift in his thinking.

I have reason to believe that he was leading a double life all of the time, as if we all aren't in some way. He didn't revile his other life though, but rather embraced it and, in doing so, came to hate Christianity and any semblance of orthodoxy. His rejection led him into depths of lust and depravity that, I think, he had held the entire time. He was merely able to cover it up, but only for so long, until it became uncontrollable again. He eventually parted ways with me and my group in a large fall-out due to his confessing something extremely dangerous to us and we informed out youth-minister about it. To this day I feel somewhat guilty about revealing what we did, but I saw no other alternative as he was not turning from his sin and was trying to involve other people in it, friends of mine, and drag them down with him. *shrug*

I mention this because your guy and my guy seem to share a similar characteristic; they both love devisiveness. My guy would always argue, and hold to any stance he could in order to argue with someone else or divide them. He would hold to extremes out of mere enoyment and then, I think when it wasn't appealing anymore to hold to an orthodox Christian extreme, he flopped over to liberalism to fulfill his desire for controversy. Your guy sounds a bit like this.

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Andrew DeShazo, Deacon, Associate Reformed Presbyterian Church, Memphis, TN
"All of us stumble in many ways, but if anyone is never at fault in what he says, then he is mature, able to control his whole body."(James 3:2)