His friends didn't understand what his glider meant to him.
They tried too, sure. Katara more than the others. But they didn't understand at all.
To them, his glider was his tool, his signature. It was how he had fought, before he learned the other elements. It was how he flew, how people knew who he was. (If the tattoos and the clothes didn't give it away first.) But it was also nothing more than a piece of wood and some scraps of cloth.
But to him, it was so much more.
After he had discovered what had happened to his people - his family - his glider had become so much more to him. It had become one of his last mementos of his past life, a hundred years ago. So he treasured it more than he would have before he had ran away. When he wasn't using it for fighting, he would treat it tenderly, as if it would break if he held it the wrong way or put it in the wrong place. Once, Sokka had treated it too roughly, which had made him snap and yell at the Water Tribe boy in the same way that Katara had yelled at him when they had first started waterbending (only angrier). Katara had gotten frustrated, and had tried to give him a lecture, which resulted in him yelling at her as well, and then flying off for a solid two hours, during which he had hugged his glider to his chest and thought of what he would eventually have to return to.
They had been rather nice about it, pretending that the event hadn't happened. Sokka had apologized, but he could tell that Sokka hadn't really understood what the big deal was. If he had tried to explain that it would be as if Sokka had lost his boomerang, it still wouldn't have been the same, because Sokka could just have just gotten another one.
But he could not. Because he hadn't made his glider, and he had no idea how to make one. Even if he had known, it wouldn't have been the same.
It was like Katara's necklace. But different somehow.
As he had stared at his glider, fabric torn and ruined beyond repair, he had felt horrible. He had felt broken, like his glider. It was ruined and broken and torn, and it was his fault! If he hadn't had insisted on being a ridiculous idiot, it wouldn't have been destroyed - he wouldn't have lost the last thing that connected him to his past life. Besides Appa and Momo, of course.
But, many years later, watching his second born son, his only airbender, flying through the sky on his own glider, all by himself for the first time, he felt the hole in his heart repair itself.
Don't have an explanation for this story... sorry for randomness. But I felt that Aang's glider had more meaning to him than what his friends think. After all, it's one of the only things he has left of his old life, besides Appa and Momo of course.