Question for you: How would you like it if a man made a sex bot after you? Another question: Would you like a man who isolates you from your friends and keeps you in the dark?
That's a partial reading. Spike made the Bot for reasons other than just sex. How would you feel if a man used emotional blackmail to gently coerce you into turning yourself into an inanimate object? From Intervention:
BUFFY: "Yeah. Strength, resilience ... those are all words for hardness. (pause)
I'm starting to feel like ... being the Slayer is turning me into stone".
Moreover, coerced you when you were still grieving. There's reason this conversation with Giles begins the episode with the Bot. The Bot has little long term effect on Buffy. In contradistinction, I'd say the conversation with Giles clearly marks the beginning of her "depression". In the absence of a statement from a trained professional, all evidence points to Buffy's state of mind being Melancholia. Melancholia's a deep depression often linked to a failure in the mourning process. More theoretically, it's used by certain schools of feminist thought to figure the psycho-social processes that create a schism between mother/daughter and perpetuate female oppression. They use the Bot to replace the Slayer - which suggests both are automatons. What it doesn't (really) replace is Buffy. That said, we see Dawn cuddling it; we see Tara trying to rationalise with it; we see Willow explaining things to it. I think it raises questions about what constitutes "human".
He doesn't really try to separate her from her friends. Rightly or wrongly, she separates herself. She's on a flawed therapeutic journey. Perhaps with the best intentions, IDK, she refuses to talk to her friends. Instead, she enters into dialogue with a man she bars from speaking (she only gets some sort of clarity when she's forced to talk) and whose words she rejects. In the beginning he tells her to go back to them. He suggests she tries his world. In fact, he's a "dirty thing" who wants her to come clean about this "thing" they have. He wants to be in her world. Don't be fooled by the "light/dark" binary. You can't "see" (a common metaphor for "know") in full darkness but you can also be blinded by light. This metaphor is central to S7. Hand in hand, they create an alternative "enlightenment".
It occurs to me to wonder...how much of Spike in season 5 on is actually "pure Spike" and not "mind-altered Spike by the monks"? The spell affected him as well, and he was protective of Dawn even early on in this seasons. I think it's a relative question for this thread about Spike's overall behavior.
Being in love is often figured as under a spell - mostly, I think because we don't feel "in charge". Western thought doesn't like the idea humans aren't rational with full autonomy (unless we're talking about divine determination). However, for me, there's enough textual evidence to support non-magical processes. His feelings for Buffy can be inferred from his psychology (out of his mind); his past history; and the other discourses the text brings into play. That said, were your "head-canon" be confirmed, I could accommodate it.
In answer to the OP - yes, he starts to change before the soul. The chip acts as a rudimentary "yes/no". It applies the same sort of logic a parent uses with a young child (yes/no - because it is). He'll find loopholes and he'll test against the reality principle (as a child does) but his "growth" has already begun.