My grandchildren tell me this is not at all uncommon. Kids are having sex in grade school even. But it breaks the heart of any parent!
Two good things to consider - one the kid has been honest and upfront with you. That is a real plus. He doesn't want to put on a facade at the KH - or represent himself as what he is not. There is a whole lot of commendation for his sincerity and truthfulness before God. And two - he feels confident enough of your love to tell you straight out what is going on. That is a grand tribute to your "unconditional" love - it is impossible to work with a liar. So your child has HOPE.
My suggestions are to try very hard to have a heart to heart about what he may think God's views are of the situation. Not to condemn - to get him to reason for himself. Kids at 14 are not dumb - they know how to put themselves in someone else's shoes and imagine what it must be like - ask him what he could do to best please God - or even if he wants to please God. Emphasize God does not force anyone to behave in a specific way - he has given each of us freedom - but he does desire our best. He does give us counsel for our protection. I don't know just how to pull this off without making it look like a "shame on you session" - that you don't want at any cost. But there has to be some way to get him thinking about his loving heavenly father and about why God gives us advice not to do things that look like fun - and feel good at the time. Talking about the tree in the Garden of Eden - how it was desirable to look upon and turns out it even tasted good as fruit and she didn't die "on the spot." Get him to tell you how he feels about that story - what he thinks Eve could have done differently - was God really withholding something good from her? Etc. Etc. He will be sharp enough to make the application without the subject even being mentioned. But get him thinking and focusing on God - that is the only thing that will ever change the behavior that I can imagine.
What would have happened had Eve run back to Adam and said "You know what the snake said to me today? Adam, that tree is so pretty. Come on let's just look at it!" The thought I want to implant in his mind is it might have been a good thing to come and talk with you first about his desire. You wouldn't have killed him for having the desire. You would have explained that is the way we are made. Yes - it is a natural thing built into us. But now let's look at the long range of things - is there any advantage of delaying this activity? Etc. Etc. Get him to tell you how he feels - more than you giving the advice. If you can get him to talk it out - there is something about saying things out loud to another human being that makes us think better. He may come to some important realizations all on his own without you ever having had to "tell him so!" Somehow mom and dad just telling us stuff doesn't reach the heart. You have to get him to think for himself - questions, questions, questions. Isn't there a proverb that talks about pulling water out of a deep well? That's what couseling a child is like.
Maybe talking to him about your own mistakes and how they have turned out - that is something very real he can relate to - everything isn't all bad ever - but there is always a better way to have done things and how does he think you could have done things better. Be prepared to bite your tongue on this because he'll probably tell you things that you don't want to hear but he will make the application also to himself in so doing.
And never stop praying for your children no matter what they do! No matter how incorrigible they seem! God doesn't give up on us and He is our example.