Why did buffy and spike have sex in the sixth season?
Being with Spike was a punishment and a distraction for Buffy. Spike was in love with Buffy but she was using him. Because of Buffy’s return from Heaven, she felt cut off from her friends but could confide in him. She also felt empty and that she didn’t deserve to be loved. Being on earth again, with problems again, was hard for her to deal with and being with Spike distracted her from her problems for a little while.