Buffy with a dark past and roommate is Spike

I can't remember the title or author of this story but Buffy has a dark past in which her mother basically neglected her. Her mother dies and she is left in custody of her sister Dawn who is traumatized by Joyce's death. Spike, who is a case manager and her roommate, tries to help her with Dawn and her past. And of course they get together.

This one?
Summary: We are all shaped by our past. But does it necessarily define who we are or who we become? Upon the death of her mother, Buffy Summers finds that the life she created for herself is going to suddenly change.

Spike has a Child Protection job... Dawn is in this story, too (I've checked for the name).

It's been a long time since I've read it but if this is the story you're looking for, then it is:

Mindstorm by WilliamsGirl

Yes, that's the one. Thank you!