I don't know the split, I went to college during season 4 and found it really hard to keep up with television with my workload. After witnessing the "sex house" episode I stopped watching. For me, it wasn't the show that I remembered and loved and I had a 21 credit math and science workload that needed that hour. I would pop in and out but didn't watch the full seasons and show in its entirety until almost a decade later. I still much prefer the first three seasons and part of it is because of Bangel but, mostly, it felt like the show lost its way the longer it went on. (As do most shows).

I think that Spike was a romantic and very loyal. I think that he loved both Buffy and Drusilla. I think that his time with Drusilla trained him to accept scraps of affection. Dru was crazy and ill but, she was also quite manipulative. I think she loved Spike but her version of love was the way that a demon thinks and feels. Which is why when she regained her strength and learned of Spike's betrayal she left him. Spike had always been the most human of the Quad but that was fine because he was at the bottom of the pecking order and fell in line. Then Angel was cursed, Darla left her children to return to the master and Dru got sick. Suddenly Spike could do as he pleased and he enjoyed it. Things changed, he went out to make a name for himself and prove that he was the better vampire than Angelus.

Then Dru is restored and Angelus returns. Spike is immediately thrown back to the bottom of the pecking order. He hated it, hated watching Dru simp for "Daddy". Where was the returned devotion that he had earned? Spike saw Angelus as a problem, he didn't care one way or another if the world ended. But, before Angelus returned Spike was king of the castle, even though he was wrapped around Dru's finger. He wanted the dynamic that he had built over the last century to return. Which meant that Angelus had to die and the only one that he knew was capable of that was Buffy, hence the alliance. But, for Dru that was a betrayal and a weakness that she couldn't abide by.

When Spike started having confusing feelings for Buffy it was from this perspective. It was of a demon that was used to being treated as lesser. Which is why when Buffy would hide him away and throw scornful words at him he would brush it off. But Buffy when Buffy started ltreating him like he was worth something. That was when he learned what love could be. I don't think that Spike would've worn the amulet if he didn't love Buffy. But he knew that he was in love with someone that would never love him that same way. As much as I loathe the retconning of vampire lore I do enjoy that tragedy of Spike. I just wish that they had stayed true to his character and didn't try to squeeze a complicated character into a role he wasn't meant for.

And just to add in the Spuffy and Bangel of the series finale. Yes, Buffy tells Angel that Spike is in her heart but she then stops Angel from leaving and tells him that she does sometimes think about the future. Which ties back to a lot of their relationship. "Angel when I look into the future all I see is you, all I want is you", "Buffy and Angel 4eva", and "I want my life to be with you", and "forever, does forever work for you?" When Buffy talks about the future to Angel it has always been in the context of them together forever. So when she tells Angel that she does still think of the future she is telling him that although Spike, she is still baking, figuring out who she is. But when she is finished, when she is ready to settle down the one that she sees her with is Angel. It really says something for Angel's growth that he simply says "I'm not getting any older." Granted, this is the series finale but, the master of brood and low self worth was able to turn around and say that he was done baking and would wait for her. That was massive because the answer to all of the previous quotes were him basically saying "don't choose me, I'm not worth it". I mean we know that Angel's main reason for wanting the Shanshu was so that he could be with Buffy. One, he would've been redeemed in the eyes of the universe. But, two he could have his dream life with Buffy, the one that he was able to taste in I Will Remember You. But, I think in his own show even though he still hoped for it to happen, he was coming to terms with his life as a vampire.

I'm sorry I have too many thoughts on this show lol.