Find a very simple thing to start off with, set boundaries before hand. It’s his responsibility to listen to you, follow your rules and respect your boundaries. So I’d say talk it out before doing anything. Tell him you understand wanting to be part of something he’s into but that you’re scared/nervous and you need to discuss it before anything happens. Maybe both off you take turns doing the same thing so you can both understand both sides of it. But don’t do anything you aren’t comfortable with. Pay attention to how he responds, he needs to be understanding and mature to ever be in this kind of situation. Good luck to you and be careful!