With no substantiation in this matter beyond a gut feeling and the knowledge of Giles' feelings and suspicions about Spike, and his disapproval of Buffy's relationship with him and, most likely, Angel as well, though that was never actually mentioned, I have always believed that the entire "Buffy doesn't trust you" speech that Andrew gave at the end of "Damaged" was part of a plot by Giles to be sure that Buffy both never knew that Spike had returned, and didn't have any further contact with Angel. All that we are told concerning Buffy's feelings about Angel and his decision to run W&H came from Andrew, who said at the beginning of the episode that he worked for Giles, not Buffy, and that it was Giles, not Buffy, who had sent him there to find Dana. It very well could be that Buffy never knew anything about Angel and his bargain with the Senior Partners, or even about Dana herself.
Later in the season, when Angel was trying to contact Willow to help with Fred, he had to call Giles, not Willow herself, a fair indication that he had no way of directly contacting any of the Scoobies directly, and it was Andrew again, (probably still working for Giles and acting as the "handler" for the Slayer we learned in Season 8 wasn't Buffy at all, but an imposter posing as her for some reason) not Buffy herself, who told Angel and Spike in "The Girl In Question" that she had "moved on" with the Immortal.
(I could go on with my conspiracy theory, but it goes far beyond the original question here, even on into Season 8, and would almost certainly go off topic)