stupid

I did something really stupid yesterday. i somehow forgot my friend's birthday. He didnt say much, he just said you forgot something...then i realized what i have done. i feel terrible, but i didnt know what to tell him. what can i say to make it up to him...i havent got a clue. he has been with me through all my sorrows and hurts...i just cant believe that i actually forgot. i really feel bad...i m sorry...