Heartthrob - S3-E1
Wesley: It's sad. The only way some people can find a purpose in life is by becoming obsessed with demons. By the way, Gunn, technically that wasn't a Lurite, it was a Murite, a subspecies of the Lurite. The male sports a small telltale fin just behind the third shoulder.
Gunn: I'm so glad to know we're not the sad people obsessed with demons.
Answer: Due to his epiphany, Angel basically had the 'true darkness' he worked so hard to reattain ripped away from him, like his soul was after sleeping with Buffy.