Xander really is a dick most of the time. Don't know why he's supposed to be "The Heart" of the group. He's mindbogglingly selfish most of the time.
It's quite astonishing. I can understand why some fans loathe him.

Although, I like him for the most part in S7...
Yes, he grows up. Which is one of the really good things about such a longrunning show. The characters get to grow and evolve.