Escalation!

The main character has rather masochistic tendencies.
One day he plucked up the courage to admit that he'd like to try dominance.
But just when he was busy worrying that She would be disgusted with him for asking for it, the response was motivated.
It wasn't long before they began their BDSM sessions.
Once they opened their hearts, dominance and submission were created naturally.
The relationship gradually escalated.....