From my perspective, Willow makes a great friend for Buffy. Xander really irked me when he was dishonest with Buffy about what Willow had said in her message to Buffy. After all, it is my honest opinion that a friend that is honest and yet nice about it is a good friend to have. Of course, a friendship cannot be built on dishonesty; it takes good qualities like compassion, honesty and loyalty to build up a friendship and make it grow stronger through the storms and fights of life, no matter how many there are in this life.
I would look at the friendship between DJ Tanner and Kimmy Gibbler from the TV show Full House
as a good example of that. Their friendship has had its ups and downs, but they managed to work things out with each other and also apologize to each other if either one of them did something wrong, too. Now that's
a strong friendship right there if there ever was one. :)