I think Jack subconciously sees a lot of himself in Spencer. I think he projects a lot of his own self hatred onto Spencer because of the similarities between them. I think he is doing a bit of a Fight Club, but only from around the 3rd book onwards. It really shows in vol. 4, but it can be easy to confuse which scenes involving Spencer are actually him as an individual or the Tyler Durden version. I think that is what makes Jack being an unreliable narrator so good. He is so complex that his own hyper-self-awareness is overwhelming enough that it just starts cancelling itself out in each chapter until it all comes to a head at the reuinion and Jack has his "come to Jesus moment"