One common theme I've noticed in my NDE studies is the fate of "back-sliding" Christians. Not only do they end up in Hell, they go to a particularly painful area of Hell. Their torment is much worse for having once believed, then turning their backs on the Almighty. In fact, it would have been better had they never believed in the first place.
I pondered upon this a while, then it made sense. Non-believers fail to return God's love because they simply don't believe He exists. A back-slider is basically saying, "I know you, Lord, but do not love You". It is more than non-belief; it is rejection. We all know what if feels like to undergo rejection. Imagine how God feels, the ultimate rejection.