I'm guessing you might be a bit young. I'm 38 now, dealing with SZA some 20+ years now. Even without the illness part of it, I know people grow apart over the years. I'm sure you'll find other friends over the coming years...some friendships even deeper than this one now that you're afraid of losing. It happens. I have a buddy I've known since before 1st grade (christ, what, 30 some years now) ......we're not best friends/so close...but we've been through enough to know that kinda connection don't come around often. Still, I have other buddies I hang out with much more frequently than the one buddy, previously noted, I grew up with and used to hang out with.

Just saying, if this friendship fades a bit, I have hope you'll find someone else and more to take the place that friendship has/had.