The books mainly focus on Harry, Ron, and Hermione (with occasional dalliances towards other students, primarily when they interact with the main trio).

That said, there's ample evidence that sex (or at least the preludes) occur at Hogwarts. As others have said, there's plenty of references to people kissing ('snogging') and similar 'PG' activities, which indicates that the awkward teenaged romances are occurring.

Moreover, in Book 4 (Goblet of Fire) during the big party there is a scene outside, where Harry observes two people (who I believe to be Moody and Snape) doing rounds of the ground. Snape blasts a set of bushes and is then seen deducting points from two students (whose names escape me), a boy and girl, who were clearly up to something.

The books mainly focus on Harry, Ron, and Hermione (with occasional dalliances towards other students, primarily when they interact with the main trio). They don't really pair up much with anyone in the series. Hermione's daliance with Victor Krum isn't implied to be sexual, just romantic, and takes place largely off-screen. Harry doesn't pursue anything of the sort, due to Bigger Things Happening. Ron is largely unsuccessful in his romantic endeavors, due to his obliviousness.

That said, there's ample evidence that sex (or at least the preludes) occur at Hogwarts. As others have said, there's plenty of references to people kissing ('snogging') and similar 'PG' activities, which indicates that the awkward teenaged romances are occurring.

Moreover, in Book 4 (Goblet of Fire) during the big party there is a scene outside, where Harry observes two people (who I believe to be Moody and Snape) doing rounds of the ground. Snape blasts a set of bushes and is then seen deducting points from two students (whose names escape me), a boy and girl, who were clearly up to something.