I agree, you need to have a long conversation with him. That being said, My 2 cents to this is perhaps He feels at a loss because He has chosen the Dom role and allowing you to top Him makes him question his role the more he thinks about it.
Best of luck to both of you,
I'm the One your mother didn't tell you about
This is what came to mind.
You mention you've discovered enjoying more than you expected, he may be in the same boat. Or he feels guilty in some way.
Fake the heat and scratch the itch
Skinned up knees and salty lips
Let go it's harder holding on
One more trip and I'll be gone
~~ Stone Temple Pilots