So, it's more than a purely physical challenge. You have some background thoughts that probably act as a psychological barrier above your anxiety to be touched. I'm not good when it comes to relationships, but it seems that you assume things, and project your fears. From your description, I think he is the one who must be afraid that you would leave him.

I think many relationships go through this phase when the future is not certain. But you have somewhat negative view of yourself. You doubt if you're good in anything. You doubt if he truly loves you ... etc. You seem like a logical person when writing, and I think you can evaluate the situation more accurately when your mind clears from the stress. I guess you have enough anxiety and stress finishing your dissertation now.