So much to be said here......Yes, two grown ups, outside of marriage, may freely consent to have intercourse. If they know that that is a sin of fornication--and it is pretty hard not to know that if you have any sense of Christianity--they will have the joy of burning in hell together for all eternity': thirty seconds of "heaven" for an eternity of hell.
Anything else is simply not a Christian or Catholic response, regardless of what some 'Christians' may say or do.
I am gonna rant again, like I did about women's clothing yesterday..........I am absolutely disgusted with any woman, if viewing her profile, who 'disagrees' with 'Church teaching' about premarital/extramarital sex. You wanna know what I say to myself when I get emots from such, or am viewed by such when I discover their thought on this? "Get away from me!!!" I add something else, also, not profanity, but I should leave it out...
NOW, the sexual act is but a small part of human sexuality. Sexuality can be expressed--man and woman each in their own unique, God-given way--in a multitude of ways. I am sure most of us know this. Expressing our sexuality as male or female goes so far above the merely physical, copulatory dimension. Thanks be to God! Of course, there is something in the human person that still inclines to that expression--let's not kid ourselves here--and all of us (males especially, generally speaking) feel that lack of expression, and perhaps the need for that expression, from time to time. But that is where chastity comes in, right. That is where our love for God and our Lady and St. Joseph come in. And this is expressed in prayer.
I was a monk for over 22 years and I guided many novices through such waters. And let me be clear: our prayer life can be and should be an exression of our sexuality. Yes, did you hear that? Look at the Canticle of Canticles in Holy Scripture. What is it about? A few things: The love of man and woman and their longing for union, set to poetry. Allegorically, it is a poem about the love of God and the love of man and their union in supernatural charity. Yes! my prayer life--and i take it very seriously--is a very real expression, daily, of my sexuality. At daily Mass and my Holy Hour..........
Our sexuality is like a pallette of paints, and our life is the canvas. If we want to paint with the 'color of copulation' only, there will be no picture: only something frightfully similar to much contemporary art........If we use all the colors in the spectrum of our sexuality (to shift the metaphor) to paint our lives, then we will have something beautiful: sexual intercourse or not.
But this requires an absolute committment to the life of prayer, and I don't mean just weekly Mass and mumbling morning and nighttime prayers...............Remember God is the best psychologist. And He knows that we are sexual beings, and He invites us to the life of prayer. That is much better than 'thirty seconds of "heaven"'