Blood Money - S2-E12
Trivia: When the Special Guest TV Stars come out and "rob" guests of their donations at the ball, one of the starring ladies is asked "What's the deal with making your character a lesbian? Is it for ratings?" A little jab at Willow's coming out on "Buffy the Vampire Slayer"
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.