Cinders, You certainly have a problem...it's going to be hard not to break his heart. You might want to say something like this:
"J, thank you for taking the time to come over and hang the shelves for me. I really appreciated it. J, I think you may have misinterpreted my intentions about things, but I'm not interested in getting serious w/anyone at this time. I need time and space to figure out who I am and I do not want to see you get hurt in the process. If you can keep things on a friendship level, that's okay, but I'm not ready for anything serious."
Cinders, you may want to play with this a bit or use something different, but you've got to nip this in the bud before it goes on any longer.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.