After someone confesses his or her romantic feelings in a friendship, things are rarely ever the same, even if those feelings are reciprocated. In this situation, where you don't feel the same way about your friend, things will definitely be different and, more than likely, a little odd for a while. There are, however, some things you might want to try to help keep your friendship stable, and perhaps in the long run strengthen it.

My advice would be to be honest with your friend. You might tell him exactly what you told me: that you care about him deeply but aren't interested in dating. You might also let him know that you are happy with the current friendship and stress that your concern is with doing damage to that.

Although being honest is probably the right thing, it may initially hurt your friend to hear that you are not interested in dating. He may very well be upset with you. This is natural; nobody wants to be "rejected." It may take your friend a long time to get over the romantic feelings he has for you and the awkwardness of rejection. And you should probably try to give him some time and space to deal with his feelings and make some (not-so-obvious) efforts to help him feel less awkward.

Most likely, your relationship has changed---at least for the moment. If you two are as close as you say, your friendship may recover from this romantic threat. Perhaps you will both be able to laugh about this crossroad in your friendship at some later date.