Here are a couple quotes:
Sexual intercourse, despite what the media would indicate, is not an indoor sport. It is the ULTIMATE expression of love between a husband and wife. Sexual intercourse, despite what the media would indicate, is not merely a physical act.
Because of the sacredness of marriage, because of the sacredness of our bodies, and because of the sacredness of our sexuality, any misuse of sex is tragic and detrimental to our spiritual lives. As Catholics we are called to be an example to others in the world.This is essentially the message of the Generation Life missionaries, some of whom are now in the diocese of New York.
A related article is this one by John Garvey president of Catholic University of America in which he reiterates the reasons for his decision to institute single sex dorms on CUA's campus