I think that, basically, Season 8 finally depicts the fate of many such friendships, especially in high school or the military. Once the main thing that binds them together is either eliminated, overcome, or simply moved on from,the real world intrudes, the friends grow up, priorities change, and the "old gang" either fades away entirely, or at least partially, changes. Xander is still helping Buffy, but we see before too long that Buffy no longer sees Xander the same way that she did in Sunnydale. Dawn is a big girl now (no pun intended) with an adult relationship and adult complications to go along with it. Willow is off somewhere with Kennedy. Giles and Buffy, for some undisclosed reason, aren't on speaking terms. Each person now has their own life, and it is separate from the rest of the gang.
Do they still love each other? Absolutely. Are they still "there" for each other? Certainly. Will they still come together in time of crisis? Without a shadow of a doubt. But the old Scooby Gang probably died along with Sunnydale. "Scoobies: The Next Generation" may consist of the same people, plus a couple more, but their lives have, of necessity, changed, and I doubt that they would ever be able to be the same group that they in Sunnydale.
There's nothing bad about that. It's just what happens when you grow up.