Reading this got me thinking that his passivity may have grown out of growing up with his possible genetic condition. The feeling that there is nothing I can do about this, so he simply resigned himself to whatever happens. People come into our lives for a reason, you have to discover what he has to offer you in your growth and what have to offer him. You've already moved him to take what is a huge step for him - getting tested and learning he doesn't carry this condition. That may or may not be what you have crossed his path for. He may need time and different opportunities now, to move forward with this new life view.
What has there been here for you and your personal growth? You've held your ground for what you needed to know about him and that is positive. You say you "desperately want to be able to depend on someone". Perhaps that needs rethinking? Maybe lose the "depend" and the "desperate" (I have my own "desperate" - so understand the feeling) think more of someone to be a partner? It's that vocab thing, different feeling to the words.
You are right, if he is resigned and requires guidance and leadership in everything, he would be a scary man to have children with. What he may need is some one who is less strong than himself or better yet to be in a situation where he truly has to depend on himself. Perhaps you need to be able to learn to let others find a way? Rather than leading or guiding? I don't know, Just throwing out some thoughts.