Well, there's a big difference between Willow/Xander and Oz/Veruca - all Willow and Xander did was kiss, while Oz actually had sex with Veruca. Granted, there were extenuating circumstances in Oz's case, but still, having sex with someone else is completely different from just kissing someone else.

But, that said, in the aftermath of the Clothes Fluke, I do think that Willow was a lot more concerned about how she felt than she was about how her makeout sessions with Xander had made Oz feel. And that ties in to the reason I never shipped Willow/Oz - it was obvious, to me, that Oz cared very deeply for Willow, but I just never got the sense that Willow cared all that much about Oz. I kinda would have liked Seth Green to have stayed with the show so we could have seen that dynamic play itself out - but then we wouldn't have had Tara, who I love, so maybe it was for the best after all.

Even though I was always a Willow/Xander shipper, I still felt kinda sorry for Oz, though.