How do I break up with my roommate/boyfriend?

I thought I was in love, but now I realize I was just infatuated with this man. We both thought it was going to be forever with us. We moved in together, signed a lease. Now I am not attracted to him at all. I still want to be his friend though. But that's all there is left on my part. On the other hand, he is still crazy about me. I am 25, so I should have known better to have not gotten so silly about all of this. I just got caught up in the moment and now I'm paying for it. I feel so bad about all of this mess. I don't know what to do or how to break it to him. I don't know even the first words to say. Everytime I try to bring it up, I do it wrong, and we end up still together. How can I say to him that I don't feel the same, when just a month ago I was head over heels "in love?"