Um, there aren't many relationships in that show where someone hasn't killed or tried to kill their significant other.
Well, I don't like the other relationships between mortal enemies either. Xander/Anya is probably even more ridiculous than Spuffy in that respect. The sheer existence of those two ships breaks my suspension of disbelief into a million pieces.
Things like Wolf!Oz trying to kill Willow are quite different, IMO. And there is Jenny/Giles, Buffy/Riley, Xander/Cordelia, Willow/Xander, etc. without anyone trying to kill the other