Darenimo Naisho de.

From Hoshikuzuu Scans:

Maki, a popular and good-looking dude, but a virgin. Despite his playboy looks, he believes that sex should be done with someone you like. A pure-hearted teenage boy that you rarely see nowadays. And by some accident, his classmate Miyashita found out about him being a virgin. In exchange for his silence, Maki is threatened into going out with him. He reluctantly accepts, but later discovers that Miyashita is a huge sadist.