How to get my boyfriend to go down on me?

We've been together for a year I'm 20 and he is too. We lost our virginity to each other last January and pretty much had sex and fooled around in every way possible except for the fact he won't eat me out. He's olny tried once and I wasn't even the one who wanted to try it he was, he even begged me. After that one time he's never done it again and I just want to know how I can bring it up. I really liked it when he did but I'm just too shy to say it, what should I do?