You COULD try it, but if you don't, then PLEASE don't lead him on. Honestly, I was in a situation where I had very very strong feelings for someone who...well, wasn't into boys, but I didn't know that for a while. I clung to this bloody hope of a relationship because I interpreted her friendly smiles as flirting, just to have some hope, because I didn't know anything and I couldn't just ASK her...and in the end I just kept on trying and failing to get over her. It's been three years now and I'm STILL not over her.
So, if you're really sure that you're 100% into girls, not willing for any boy romance, please be upfront with him. Tell him gently, and sweetly, but still firmly and bluntly--if he's your friend, you don't want it to hurt any more than is necessary, but you also want to give him 100% clarity.