Complex sentence: The chip does not affect him when he harms demons, and he often fights on Buffy's side, if only for the pleasure of brawling, though his motivations changed when, in the fifth season, Spike realized he had fallen in love with her.
Split into simpler sentences: The chip does not affect him when he harms demons and he now often fights on Buffy's side, at first just for the pleasure of brawling. His motivations changed when, in the fifth season, Spike realized he had fallen in love with her.