I am sorry to hear about your situation. I am also in love with one of my bestest friends, but he has a long-term girlfriend. He knows how I feel know. It seems like whenever we talk know, he has to bring her up to remind me (or himself) that she is still in his life.
My best advice to you, is be his friend. That may be what he needs the most right now. Like others have said before me, he may turn out to be your best friend in the world!!! I know it isn't what is what you want, but at least you still have his friendship.
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ZTA
"Even in our sleep, pain which cannot forget, falls drop by drop upon our hearts. Until against our will comes the wisdom of God."