i don't think its hatred.. by my point of view,spike never was good enought for womens and all when he was alive, when he died , he saw the opportunity to start again with his new "family", but angelus in asorta of a way keeps pushing him down, because he wasent "evil enought" for him... so in a way angelus wanted spike to be more like him, and spike eventually wanted to become more like angelus, (drussila thing..) so i a weird way, angelus is somewhat responsible for what spike becamed (when evil), and when he got his soul, spike reminded of him when angelus.. so angel can't stand respect and be friends of spike becaus he feels that the way spike is alike angelus , angelus hates angelus so angel feels he should hate spike...
and spike wants to hate angel because he feels angelus was responsible by what he become (i only agre at it at some point)..
the buffy thing just mess it up more, angel and spike both love buffy, and angel left her so she could be normal, but inside he still thinks they would end togueder. by involving herself w/spike, angel feels like he's been betraided somehow, and that the new "ensouled" spike might not let the bangel final he though it would become.. the fact that spike got his soul by his on will only frustrad angel more, because he's not responsible by his actions when angelus, and spike still souless try to reddem himself..
spike on the other hand thinks that now with a soul, he is as hgood as agel and has nothing more to prove to him that they are equals.. so he has the same right to love and stay w/ buffy as angel..
i hope this makes any sense...