When does he demand her forgiveness ?! He even says that he can't say "sorry" or "forgive me" because of how wrong it would be.
He did this for her ...yes, it's true, why would he lie ? That doesn't mean he's blaming her or expecting anything from her.
I would not take the position that Spike is "demanding" forgiveness from Buffy but he seeks it, never the less. And throughout the first half of the season it is emphasized that the reason he is suffering is
because of her. And the implication is that because he did this and suffered for her that she should forgive him.
In Beneath You, Spike says that he did this "for her, to be hers" all of that monologue indicates that he thought he was going to come back and he would be forgiven, he realizes it isn't going to be that easy now, but he still wants that from her. And he ultimately gets it. Not just forgiveness, but Buffy this season is his protector, motivator, his only ally, etc. Everything he sought from the act of getting his soul - he basically gets. Basically his plan worked.
And while he doesn't have to lie to her (regarding telling her that he got the soul for her) it's not just that he says "Yeah I went and this for you." It's that he tells her in great detail that his
pain, suffering, and torture is because of her. When, reality check, Buffy never asked him to go get a soul. She broke up with him tried to move on with her life and he didn't like it. When he realized he couldn't force himself back into her life (AR) he went and sought out the only other desperate option there was. If he went and got a soul, that sounds like a personal problem. Only it isn't. It becomes Buffy's personal problem. And Spike wants her to know exactly what a big deal it is. In Never Leave Me:
BUFFY How did you do it? How'd you get your soul back?
SPIKE Saw a man about a girl. (sighs) I went to seek a legend out. Traveled to the other side of the world, made a deal with a demon.
BUFFY Just like that?
SPIKE No, not just like that. There was a price. There were trials, torture, pain and suffering... of sorts.
BUFFY Of sorts?
SPIKE Well, it's all relative, isn't it?
BUFFY Meaning?
SPIKE Meaning I have come to redefine the words pain and suffering since I fell in love with you.
It's not enough for Spike to tell her that he got his soul he has to paint the picture for her too. And why else would he do that if not to make her understand the magnitude of this "big thing" he did for her. What other motivation could he have than to hope that this would lead her to forgive him or accept him? Also, he is - sorda blaming her here. He is saying that he is suffering because of "her" love.
I understand that many people read this to mean that now that Spike has a soul, he knows pain and suffering. But the problem is he doesn't need to place the weight of that pain and suffering on Buffy. He is in this position because of the actions of his own demon - NOT BUFFY. She has her own problems and once again - she never asked him for this. She owes him nothing and yet it's implied that she does because he is in this situation "because of her." I think Spike actually has this realization in the comics at some point and I commend them for going there. I'm glad that after s7 Buffy spends some time apart from him.