If Buffy had noticed how miserable Willow was beforehand she could have been able to prevent it. Though Buffy herself was also miserable and so that's probably why she didn't notice. If Willow had noticed how miserable Buffy was, then Buffy would have felt supported enough to be able to notice that Willow was miserable... etc. I think their propblem was that when they were miserable they tried to deal with it themselves rather than going to their friends for help and support.

why didn't put dowen i be pisss because almost destier the earth

Then again, if I was Buffy, I'd still be tripped out about having been dead for like 3 months and kinda not feel it (like she does)