Well, this isn’t just an “online” condition, created by a bunch of hypochondriacs. This is a documented syndrome with decades of clinical history with a number of peer-reviewed journals out there. Educate him. Pull up journal articles. Pull up books written by Dr. Crook, Dr. Crandall, Dr. Truss, Dr. Hyman, Dr. Sehnert (Candida-Related Complex). Educate yourself. The more you understand it, I mean really understand it, the less you will need him (or anybody) to understand it. Allow your own healing to speak volumes to its authenticity.
Who knows maybe through this your relationship will get stronger, or maybe you will see something else.
All the best towards your healing.