Slave/Master ~Kanojo to Kanojo o Shibatta Kusari~

Shuusuke was sexually unsatisfied and tired of the game.
That's when his younger twin Yuusuke asked for advice:
"How do you get all the way to making it with a girl?"
Shuusuke's heart lifted at his brother's enthusiasm.
But not to help. He saw a chance to revive his own
libido by stealing away the subject of his brother's love.

[From DLsite english]