Emotion and Motivation

Keep your characters well-motivated. Emotional stakes may include guilt, fear, worry, shame, etc. Often this directly relates to the internal conflict.

Men's Emotional Reaction to Sex

Men might be fumbling/nervous/possessive after/during the first lovemaking because it's the relationship point of no return.

Fear

What is your character afraid of? Baring his soul? Being inadequeate? Disapproval? Show this to your reader through dialogue, action, and/or internal thoughts.