If you were sober then I'd say you were either:
1. Intimidated and scared to ruin the situation
2. Worried that you might not perform
3. Over-analyzing the situation and thinking about it sort of like a chess game, instead of going with the flow
4. Subconsciously nervous/apprehensive about the prospect of sex
5. Gay
From what I have read in your posts I am almost sure #3 is a problem for you, the others I am not sure about. Books and advice can only point you in the right direction, you still have to be congruent with yourself and the material. You seem like an intelligent, logical, guy with a love for self improvement and learning. I know it sounds stupid but you sometimes need to ignore the voices in your head and just be happy.