I could never see Ben and Buffy as a couple. They might have gone out a couple of times before realizing it, but, while I tend to disagree with Spike about Buffy needing a little monster in her man, she DOES need a little monster FIGHTER in her man, and I just can't see Ben in that sort of role. Maybe it's because I always saw Ben as the exact opposite of Glory, at least until towards the end, when the two seemed to begin blending or merging into a single entity. Or maybe I just never saw Ben as anything except the place where Glory hid when she wasn't out hunting for the Key. For whatever reason, I just can't see Ben and Buffy as ever making it beyond the second or third date.
Of course, the irony is, even when Ben was Glory's secret identity, Giles would have seen him as the perfect match for her, right up to the time that they found out the truth.