Friend Zoned

So my friend Alex. He has always been my trusty best guy friend. Sharing a name and all we had known about each other's existence for about a year before we really became good friends. I went to him for advice about everything and even just to chat. I had absolutely no idea he liked me.
His feelings for me though are so cute. It started when we were playing a guessing game to guess who we thought about the most. I guessed so many times until it was narrowed down to a girl, that I really know, and is one of his Facebook friends. Like the very slow person I am I don't catch on. He's guessing too and I really don't have anyone I think about the most besides my boyfriend. Which Alex knows I'm dating. Finally he gives up and so do I and I reveal that it was some random kid in our history class. He's like "I don't want to reveal mine :x" and I coax him and he's like "Fine I will. Eh..its you." And I'mK like appalled. Shocked.
I didn't know what to say but I can't stop laughing because I had ABSOLUTELY no idea. I told him I was stupid for not getting it.
His response: "You would've guessed easier if I said drop dead gorgeous."
"I've wanted to talk to you since the beginning of eigth grade year."
"We bumped into each other once or twice but I tried not to stare (because you were so adorable)"
I wasn't sure what to do. At all. I asked him if he knew that I was still dating someone else. And he said yes. I asked him why he said it then. "I wanted to say my feelings to the person which deserved to know them."
I completely friend zoned him. :/