James Marsters said it himself that Spike went in there for Buffy, and died for Buffy.

And as for Buffy loving Spike, she did love him. But she understood that him dying was something that needed to be done. That the rest of the world was on the line. She respected his decision. Did she want it, of course not, but she knew it needed to be done. She says herself to Spike she wasn't ready for him to not be there, but when it came down to the rest of the world, she was mature enough to realize that her feelings didn't matter.

There were many times Buffy wouldn't let Spike die, when the world wasn't on the line. In Never Leave Me, she wouldn't kill him when he begged for it. In Showtime she fought off a superstrong ubervamp to save him. In Lies My Parents Told Me she defied Giles to go save him. During season seven when he was under the influence of the first, she still wouldn't kill him.

Same with Amends, Graduation Day, and Zeppo, the world wasn't on the line.

All of late season two, Buffy's love for Angel caused her to be selfish with her denial in her duty to the rest of the world to kill him, and it caused harm to a lot of people. People died, Giles was tortured, Jenny was killed. But finally she understood she had to kill him for the fate of the rest of the world, just like the Buffy of Chosen who was in love with Spike understood that she needed to let him go be her hero, the hero he wanted to be for her. She left because she owed it to him to live the life she, and he, wanted her to be able to live.

Ok, just because Marsters said it doesn't make it so, it's down to interpretation. Personally, I don't think Spike did it solely for Buffy, she wasn't his main motivation. The amulet was Spike's redemption, his chance to payback all the hurt he'd caused over his time..his chance to save the world and everyone in it, including Buffy.

When he says "I'm gonna see how it ends", he knows that's his swansong, that's his goodbye, he's going out a hero and he loves it!

Also, Graduation Day and The Zeppo do see the world on the line. The Mayor wouldn't have stopped at SunnyD and the hellmouth opening has already once being called an apocolypse so why not that time?

Yeah, I think he did it partly for Buffy and partly for being a hero himself. There were lots of reasons; he wanted to die for Buffy, he wanted to save the world, he wanted to do the right thing, he was the only one who could do it anyway since Buffy didn't want Angel to. And I bet he loved doing something that Angel couldn't do!
I don't think it was just one reason.

And of course, I don't think that Buffy was in love with Spike (I like the idea of the line "No you don't, but thanks for saying"--great unrequited love theme), so that helped her see more clearly in allowing Spike to sacrifice himself where she wouldn't let Angel.

if yo seriously think Buffy didn't love Spike then i suggest you go back to Showtime (the scene in the cave) and tell me honestly you believe those are not the eyes of a woman in love:)

When James Marsters was asked about what buffy "love" for spike in the last episode and his responce to it "It's true," Marsters insisted. "It's the truth and he shows his manhood by saying so. Yeah. I thought that what the final episode did very well was admit that Buffy really is in love with Angel. That the sexual relationship she had with Spike was unhealthy. That it was unwise. " Yeh ^_^ spike admits she doesn't love him

Joss Whedon himself said that Buffy loved Spike and he never said who Buffy loves the most

This whole concept of who Buffy loves "the most" is kind of silly. Yes, she loves Angel. Yes, she loves Spike. There is no question of 'most'. The two relationships have a multitude of variables that make them almost impossible to compare accurately: Her age, her maturity, the number of bloody apocalypses she's averted, post-undeath emotional flailings, her sexual confidence, the list goes on.

She's cookie dough, remember? Personally, I think she's going to end up with a middle-aged, small-town dentist with pollen allergies.

Anyway, my answer to the original question is as follows. Spike is a multi-faceted bloke. Yes, he did it for Buffy, yes he did it for his own desire to be a hero, yes he did it to stick one to Angel. Any one reason does not negate the others. He knew this was his chance to be the kind of hero he thought Buffy needed. Noble, but dunderheaded, as Spike was obviously new to the whole golden boy biz. Hence the line.

Besides, I bet he really did want to see how it ended. I know I would.

I have a question about spikes heroic death how did he die Im just preparing for the upseting before I watch it so when i do watch it Im not gonna scream and kick about him dieing and it being unfair!!Right now Im mad that he even dies !!!!!!!!!!!!!!!!!!!!!!!

James Master is a great actor, but Joss Whedon produced and directed Chosen and he has already said:

"But the hands were all gelled up and you could tell so this is CGI and it looks beautiful I thought it was a nice comment on their relationship. WHAT I BASICALLY TOLD THEM WAS PLAY THE ROMANCE BE PROUD OF HIM , LOVE HIM WHEN YOU SAY YOU LOVE HIM / LOVE HER WHEN YOU SAY SHE DOESN'T LOVE YOU . forget about the crumbling world for that period of time it doesn't exist..." (Transcript, S7 DVD).

“BUFFY WAS IN LOVE WITH SPIKE THE MOMENT THEIR HANDS CLASPED.” (San Diego Convention)

And this was how to get her in the sack with Spike half an act after Angel had left but you know the experience. I've said this probably a hundred times and probably all of them on the audio commentaries to these damn episodes the trick is always to make the audience go through exactly what she's going through It's confusing to us emotionally that we should bounce from one to the other and it's confusing to her but SPIKE IS THE PERSON IN HER LIFE RIGHT NOW…”