This takes place after season 7 , but I don't remember AtV being involved. Spike makes it out of the Hellmouth and at the end PTB ask Buffy what she wants as her reward. She says something like she wishes she was normal, or that she wished she had no knowledge of vampires. The PTB grant her wish by removing her from everyone's memory. They make it so that the deeds she did were done, but no one remembers who the specific slayer was that did them. Once they finish with Buffy, they ask Spike what he wants and he first asks what did Buffy ask for. Upon finding out, he asks to be able to keep his memory of her. His wish as granted. Years pass and one day in the mall or on the street Buffy runs into him (still without memory of her past) and tries to get him to date her. Spike declines, but she is persistent so he gives in. He does ask the PTB why all of a sudden is she showing up in his life and will he lose his memory of her now that she is. They respond that as long as he does nothing to make her remember he is free from their wrath and memory wipe. So he starts dating her and before long her past changes to reflect more of her Slayer life. Eventually, she does remember and she blames him for the loss of her idyllic life before running away from him. He goes home to await his memory wipe when out of no where Buffy appears and she explains she went to the PTB and they made her see that he did stay away from her. It was she who pursued him from the moment she saw him. She admits she loves him and that his memory will stay intact and so will hers.
S/n- I want to say that I believe Buffy first sees him in a record store at the mall. Also, Spike lives above a funeral parlor. When he first starts dating Buffy he hides his blood in a refrigerator in his library/spare room. There's a scene where Buffy comes over one day and he hadn't had a chance to hide his blood and she pours him a mug, heats it and gives it to him without realizing what she was doing. | 
