He really is just awful, and the terrible thing is that first watched Buffy when it aired, when I was 12-18 years old, and have rewatched it fairly regularly ever since, and it's only on the last couple of rewatches that I realised how terrible his behaviour is. Because Nice Guy™ narratives are so pervasive in society and media that you sometimes don't notice them or think that there's anything wrong with them. I was really worried that the Buffy writers were condoning his behaviour or sympathising with him, but I noticed the subtle little parallels being drawn with Angel, which caused me to breathe a sigh of relief!

One thing I will say is that Xander does eventually grow up and get better. It just takes him about five seasons to get there.

Did you ever watch ATLA? I feel that Sokka went through a similar kind of character arc to Xander (feeling useless because he had no superpowers, feeling that he had to perform masculinity in a certain way, growing and realising that he did have things to offer and that there is no right way to be a man), but it took him a lot less time to get there.