Spike's role in S8 appeared to be as a support to Buffy. He does come to her aid to help her defeat Twilight, and supposedly sticks around to support her. He seems like the only person who understands Buffy's decision to destroy the seed. As for this season, I'm really not sure where the writers will take him. We know he'd play a big role in her life, so whether it will be helping her raise her child or continuing to fight by her side, we'll just have to wait and see.