“Marriage between one man and one woman is the only moral cntext for sexual intimacy. This is because in marriage, and only in marriage, a man and woman freely and willingly commit their entire lives to one another in mutual love and fidelity. … Non-contracepted sex between a husband and wife is good regardless of whether or not it conceives new life, because the act completes and reconfirms their marital promises.” Cassandra Hough, in Women, Sex and the Church.
Get the book. Read the whole thing. (the publisher has a cool Adobe page that lets you read the introduction to the book for free. Check it out!)