I would suggest trying to keep him focused on other things that interest him but are more typical.
If that doesn't let it pass, as a phase (it does for some but not others), clearly define the rules in a way you can both handle.
They make more obsorbant youth pull-ons, if more expensive than the usual youth ones. If he really wants a proper diaper, see if a part diaper is enough for him; let him pull it off like a diaper, if he wants, while being able to use it like a Pull-Up. If not, I still *strongly* advise only he changes himself.
Cleaning himself should be solely his responsibility, at his age. He should be able to diaper himself, too, if his motor skills aren't severely impaired.
You two need to figure out what comfort level(s) you have, so you can get on the same page but make sure he understands he's also expected to continue maturing in other ways.
I suggest he continue to develop teenaged interests, regardless, along with taking the corresponding responsibilities.
He will probably do the binge and purge cycle, so I suggest - if he says he wants to throw it all out - you offer a big trash bag but actually store it all for him. Let him be clear he wants it back, if he's going to, before you offer it back. You'll save potentially a lot of money, as this can go on for years.
Please and thank you.
~ A long-time AB/DL who wants to make this easier for you both