I have friends that I have grown apart from, and it doesn't bother me all too much because we did grow apart. We just didn't enjoy hanging out much anymore, but there was no bad blood. I still drop a couple of those people the occasional text, and we talk that way a small amount.
Losing a friend via a falling out is awful, though, and I hate it, and it usually bothers me for years. I'd rather we eventually make up, even if it's in a small way, because normally when it's up to me, I don't end friendships because of fights. I like to work past them. Life's too short to hold grudges.