He met Drusilla, and made her a demon, and she made Spike a demon, and so on, and so on,... But, Angeles made the mistake of killing a Gypsie, and was given his soul as a curse. Ooo! I scared! He became the stink guy, and was inlisted to help Buffy.
They fell in love, they broke up, got back together, broke up, and so on, and so on, until Angel went to L.A. Bye, bye! Smooch!