There's an article you should Google - it's called "The Care and Feeding of the Introvert".
I honestly think that as an extrovert, you are probably never going to understand *why* people are exhausting, *why* too much talking wears him out, *why* he doesn't want to be forced into physical proximity against his will - but if you want to be with him, you have to move past the why and just accept that it is what it is. Either you can deal with the way he needs to live his life, or you can't.
But do read the article - it's a great intro to intros!
H: 39, Me: 37 SD: 18, S: 7 M: 9, T: 10 "I love you but am not in love with you" - 5/11 Discovered online affair - 7/11