I get that, I really do. But I just think it was so out of line considering everything that Giles has done for her. Sometimes parents (lets face it, he's always been a parental figure to her) make mistakes, but that doesn't mean you should totally dismiss them in the way that she does.
I was watching season two yesterday and it made me even more angry to think of how Giles is treated in season seven, because he sacrifices his relationship with Jenny for Buffy and it simply kills him to do so. But Buffy comes first for him. And I just think that because of everything she has ever done for him, to treat him as she does, for so long, is just, disgraceful to be honest.
And to get back on topic:
I don't think its safe to say all Bangel fans would have preferred for him to have told her. I, in fact, am glad she didn't. I don't think it was the time for it. I don't think Buffy/Angel would have reached the level of maturity they are at now, if Buffy had been told that day.