Alternative to Adultery

Heidelberg Catechism, Lord's Day 41:
Q108. What does the seventh commandment teach us?
A108. That all uncleanness is accursed of God: and that therefore we must with all our hearts detest the same, and live chastely and temperately, whether in holy wedlock, or in single life.

Q109. Does God forbid in this commandment, only adultery, and such like gross sins?
A109. Since both our body and soul are temples of the Holy Ghost, he commands us to preserve them pure and holy: therefore he forbids all unchaste actions, gestures, words, thoughts, desires, and whatever can entice men thereto.