I'll throw my two cents in as well. I am in agreement with the others. It may prove to be a good thing for you both, but before I would do anything, I would ask myself if you believe your stepson's best friend can be trusted to be discreet and keep things confidentially between you both. If not, then it may set up a situation where he tells your stepson (perhaps accidentally), since your stepson knows his friend is transgendered. They undoubtedly will talk about this. Any chance your stepson has a similar curiosity? It so this could have the potential to also become a family affair.... Good luck!
Di