On the other hand, I was in your friend's shoes once. Well, at least once. I have a rather tragically big heart, and I'm prone to developing crushes. From experience, I know that this poses a great risk to a friendship. Like your friend, I was forced to make the difficult choice of whether or not to keep my feelings secret, or make them known, and there are good reasons for each decision.

When I have decided to keep my affection for someone hidden, the choice I made was to protect her from the pressure of an expected response, as well as the consequences of awkwardness and unhappiness that would come between us. No matter the reaction that she would have to such a confession, the existence of those feelings themselves force the friendship to change, and any change from the wonderful ease and trust of a close friendship could be a bad thing.

Conversely, when I have chosen to tell someone about the feelings I have, it was because I could not bear the strain of keeping such an enormous secret from someone who expected honesty and sincerity from me as a natural part of our special friendship. It's no small thing to lie to your best friend, even if you decide that it is in her (or his) best interests to do so, and I felt that I had to be honest in order to be worthy of the trust given to me. In my case, however, I wasn't necessarily expecting, or even hoping, that those feelings would be returned. It was more important to merely be honest and attach no conditions or expectations to my confession. With that said, of course, I'm sure that no one who ever opened up his (or her) heart to another person would be upset or disappointed to find that the object of that affection held similar feelings too.

It is, of course, so much messier and tense when there are wants and expectations attached to someone's feelings for you. Despite how unfair it is, it's important to realize that your friend must feel hurt and confused too. Unrequited love is one of the most painful things to bear, because when sincere and tender affection is unreturned for any reason, it can feel like outright rejection. It's certainly easy to interpret unrequited love that way. It's possible for the strong feelings of someone in a close friendship to evolve to an even broader and more consuming level of affection -- after all, friends already love and respect and care for each other in some way. In you he probably sees a special, beautiful person that he wants to make happy in every possible way. I'm sure at least once in your life you have had a crush, or perhaps have even been in love, only to find that the person you cared so deeply about neither wanted nor returned those feelings. I'm sure you remember how disappointed and humiliated you felt -- as though you weren't good enough, and as though you didn't matter. Your friend may be interpreting your response as a statement that he is unworthy of your love -- and as a result he probably feels ugly, worthless, and ashamed. It must be excrutiatingly difficult for him to face you. He has probably convinced himself that since you don't want him as a lover, he must not be very special to you after all. Not that any of that is your fault. The most obvious hazard he faced was disappointment and heartache, and I do wish he had considered those risks before confessing his feelings to you. I have to say that, despite his pain, it was selfish to confess his feelings with the expectation that you would return them in exactly the way he wanted, and to jeopardize your friendship because the consequences are not to his liking. But I do want you to be aware of the fact that it this is an extremely difficult time for him as well, and he may come to see things differently.

Sometimes people do fall in love after they've been friends for awhile, even a long while, but not always. Sometimes your best friend is supposed to be just that: your friend. And it's not that being "Just friends," means that the friendship is insignificant, or that it is any less precious and beautiful than a romantic relationship. Instead, being best friends connotes trust, sharing, affection, and intimacy of a level that only a rare few relationships ever attain. While it's tempting to seek the best of both worlds and add romance to the close bond that already exists, it's obvious that the volatility and tension of a romantic relationship stands in contrast to the ideals of stability, endurance, and confidence that a close friendship is supposed to represent. It's a heavy gamble to risk the safety, happiness and comfort of one simply for the passion and longing of the other. Occasionally that gamble works, and two people find happiness together as lovers, but for many people who move beyond the bounds of that friendship, they can find it damaged in the long term, and hard to repair. When two people are best friends, they must be able to share almost everything with the expectation that they have in each other a confidant and a constant companion through the best and the worst that life can offer. Such friendships are among the best things that we'll find in this world.
One of the hardships of romance is that, unlike friendship, it isn't necessarily meant to last. Love is a complicated emotion, involving the greatest and the ugliest that humans can give to each other. It inspires altruism and sacrifice, tenderness and growth, it can unite two lovers in luscious passion, and love completes a lonely heart. But love can also be selfish; love naturally involves some desire to have that love returned, and this can sometimes spawn jealousy and possessiveness. Love has a way of changing over time, and this is often unattractive when weighing the advantages against the harms of moving beyond a close friendship that would otherwise last for many years. Love definitely has its dark side. People have done hurtful, or horrible, or violent, or spiteful things, all in the name of love. It's very hard to move from platonic love to romantic love, and it can be at least as hard for two people to go back to a close friendship when the romance fades without a great deal of strength, communication, and maturity. Your friend shouldn't be in such a rush to torpedo the rare goodness that you have. He'll miss it someday.

My advice to you is for you to try and explain this to him. Ultimately the decision rests with him, however, and I'm certainly not advising you to take this burden entirely upon your shoulders so that you feel obliged to do all the work involved in trying to save a friendship that may be beyond hope. If he cannot put his feelings of friendship above the love he confessed to you, then the loss of your friendship is his fault, not yours, and this will be a decision he will have to live with for the rest of his life. Talking to him about this is probably the most important thing you can do. It may be difficult for him to be your friend when he is in love with you, but that hardship was the risk he faced when he decided to profess his love for you, and if you are willing to care for him despite the burden he has placed upon you, then he has no excuse to avoid making the same effort.